auto merge of #11946 : alexcrichton/rust/no-io-error, r=brson

Turns out this was a little more far-reaching than I thought it was.

The first commit is the crux of this stack of commits. The `io::io_error` condition is completely removed and the `read` and `write` methods are altered to return `IoResult<T>`. This turned out to be an incredibly far-reaching change!

Overall, I'm very happy with how this turned out (in addition with the `unused_must_use` lint). I had to almost rewrite the pretty printer in `libsyntax` as well as the the formatting in `librustdoc` (as one would expect). These two modules do *tons* of I/O, and I believe that it's definitely improved.

This pull request also introduces the `if_ok!()` macro for returning-early from something that returns a result. I made quite liberal use of this in mostly the pretty printer and html renderer, and I found its usage generally quite pleasant and convenient to have. I didn't really feel like adding any other macro while I was using it, and I figured that pretty printing could be nicer, but it's nowhere near horrid today.

This may be a controversial issue closing, but I'm going to say it.

Closes #6163

39 files changed, 1814 insertions, 2138 deletions

diff --git a/src/libstd/comm/mod.rs b/src/libstd/comm/mod.rs
index 7b1a6055542..bccebeaa79f 100644
--- a/src/libstd/comm/mod.rs
+++ b/src/libstd/comm/mod.rs
@@ -1252,7 +1252,7 @@ mod test {
             spawn(proc() {
                 let _p = port;
             });
-            task::try(proc() {
+            let _ = task::try(proc() {
                 chan.send(1);
             });
         }
diff --git a/src/libstd/fmt/mod.rs b/src/libstd/fmt/mod.rs
index a17a030f4f7..06737e22007 100644
--- a/src/libstd/fmt/mod.rs
+++ b/src/libstd/fmt/mod.rs
@@ -163,9 +163,10 @@ method of the signature:
 
 ```rust
 # use std;
+# mod fmt { pub type Result = (); }
 # struct T;
 # trait SomeName<T> {
-fn fmt(value: &T, f: &mut std::fmt::Formatter);
+fn fmt(value: &T, f: &mut std::fmt::Formatter) -> fmt::Result;
 # }
 ```
 
@@ -174,7 +175,14 @@ emit output into the `f.buf` stream. It is up to each format trait
 implementation to correctly adhere to the requested formatting parameters. The
 values of these parameters will be listed in the fields of the `Formatter`
 struct. In order to help with this, the `Formatter` struct also provides some
-helper methods. An example of implementing the formatting traits would look
+helper methods.
+
+Additionally, the return value of this function is `fmt::Result` which is a
+typedef to `Result<(), IoError>` (also known as `IoError<()>`). Formatting
+implementations should ensure that they return errors from `write!` correctly
+(propagating errors upward).
+
+An example of implementing the formatting traits would look
 like:
 
 ```rust
@@ -187,7 +195,7 @@ struct Vector2D {
 }
 
 impl fmt::Show for Vector2D {
-    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) {
+    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) -> fmt::Result {
         // The `f.buf` value is of the type `&mut io::Writer`, which is what th
         // write! macro is expecting. Note that this formatting ignores the
         // various flags provided to format strings.
@@ -198,7 +206,7 @@ impl fmt::Show for Vector2D {
 // Different traits allow different forms of output of a type. The meaning of
 // this format is to print the magnitude of a vector.
 impl fmt::Binary for Vector2D {
-    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) {
+    fn fmt(obj: &Vector2D, f: &mut fmt::Formatter) -> fmt::Result {
         let magnitude = (obj.x * obj.x + obj.y * obj.y) as f64;
         let magnitude = magnitude.sqrt();
 
@@ -207,7 +215,7 @@ impl fmt::Binary for Vector2D {
         // for details, and the function `pad` can be used to pad strings.
         let decimals = f.precision.unwrap_or(3);
         let string = f64::to_str_exact(magnitude, decimals);
-        f.pad_integral(string.as_bytes(), "", true);
+        f.pad_integral(string.as_bytes(), "", true)
     }
 }
 
@@ -242,6 +250,7 @@ strings and instead directly write the output. Under the hood, this function is
 actually invoking the `write` function defined in this module. Example usage is:
 
 ```rust
+# #[allow(unused_must_use)];
 use std::io;
 
 let mut w = io::MemWriter::new();
@@ -468,16 +477,20 @@ will look like `"\\{"`.
 
 */
 
-#[cfg(not(stage0))]
-use prelude::*;
-
 use cast;
 use char::Char;
+use container::Container;
 use io::MemWriter;
 use io;
-use str;
+use iter::{Iterator, range};
+use num::Signed;
+use option::{Option,Some,None};
 use repr;
+use result::{Ok, Err};
+use str::StrSlice;
+use str;
 use util;
+use vec::ImmutableVector;
 use vec;
 
 // NOTE this is just because the `prelude::*` import above includes
@@ -485,22 +498,11 @@ use vec;
 #[cfg(stage0)]
 pub use Default = fmt::Show; // export required for `format!()` etc.
 
-#[cfg(stage0)]
-use container::Container;
-#[cfg(stage0)]
-use iter::{Iterator, range};
-#[cfg(stage0)]
-use option::{Option,Some,None};
-#[cfg(stage0)]
-use vec::ImmutableVector;
-#[cfg(stage0)]
-use str::StrSlice;
-#[cfg(stage0)]
-use num::Signed;
-
 pub mod parse;
 pub mod rt;
 
+pub type Result = io::IoResult<()>;
+
 /// A struct to represent both where to emit formatting strings to and how they
 /// should be formatted. A mutable version of this is passed to all formatting
 /// traits.
@@ -527,7 +529,7 @@ pub struct Formatter<'a> {
 /// compile time it is ensured that the function and the value have the correct
 /// types, and then this struct is used to canonicalize arguments to one type.
 pub struct Argument<'a> {
-    priv formatter: extern "Rust" fn(&util::Void, &mut Formatter),
+    priv formatter: extern "Rust" fn(&util::Void, &mut Formatter) -> Result,
     priv value: &'a util::Void,
 }
 
@@ -561,50 +563,50 @@ pub struct Arguments<'a> {
 /// to this trait. There is not an explicit way of selecting this trait to be
 /// used for formatting, it is only if no other format is specified.
 #[allow(missing_doc)]
-pub trait Show { fn fmt(&Self, &mut Formatter); }
+pub trait Show { fn fmt(&Self, &mut Formatter) -> Result; }
 
 /// Format trait for the `b` character
 #[allow(missing_doc)]
-pub trait Bool { fn fmt(&Self, &mut Formatter); }
+pub trait Bool { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `c` character
 #[allow(missing_doc)]
-pub trait Char { fn fmt(&Self, &mut Formatter); }
+pub trait Char { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `i` and `d` characters
 #[allow(missing_doc)]
-pub trait Signed { fn fmt(&Self, &mut Formatter); }
+pub trait Signed { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `u` character
 #[allow(missing_doc)]
-pub trait Unsigned { fn fmt(&Self, &mut Formatter); }
+pub trait Unsigned { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `o` character
 #[allow(missing_doc)]
-pub trait Octal { fn fmt(&Self, &mut Formatter); }
+pub trait Octal { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `b` character
 #[allow(missing_doc)]
-pub trait Binary { fn fmt(&Self, &mut Formatter); }
+pub trait Binary { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `x` character
 #[allow(missing_doc)]
-pub trait LowerHex { fn fmt(&Self, &mut Formatter); }
+pub trait LowerHex { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `X` character
 #[allow(missing_doc)]
-pub trait UpperHex { fn fmt(&Self, &mut Formatter); }
+pub trait UpperHex { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `s` character
 #[allow(missing_doc)]
-pub trait String { fn fmt(&Self, &mut Formatter); }
+pub trait String { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `?` character
 #[allow(missing_doc)]
-pub trait Poly { fn fmt(&Self, &mut Formatter); }
+pub trait Poly { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `p` character
 #[allow(missing_doc)]
-pub trait Pointer { fn fmt(&Self, &mut Formatter); }
+pub trait Pointer { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `f` character
 #[allow(missing_doc)]
-pub trait Float { fn fmt(&Self, &mut Formatter); }
+pub trait Float { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `e` character
 #[allow(missing_doc)]
-pub trait LowerExp { fn fmt(&Self, &mut Formatter); }
+pub trait LowerExp { fn fmt(&Self, &mut Formatter) -> Result; }
 /// Format trait for the `E` character
 #[allow(missing_doc)]
-pub trait UpperExp { fn fmt(&Self, &mut Formatter); }
+pub trait UpperExp { fn fmt(&Self, &mut Formatter) -> Result; }
 
 // FIXME #11938 - UFCS would make us able call the above methods
 // directly Show::show(x, fmt).
@@ -617,7 +619,7 @@ macro_rules! uniform_fn_call_workaround {
     ($( $name: ident, $trait_: ident; )*) => {
         $(
             #[doc(hidden)]
-            pub fn $name<T: $trait_>(x: &T, fmt: &mut Formatter) {
+            pub fn $name<T: $trait_>(x: &T, fmt: &mut Formatter) -> Result {
                 $trait_::fmt(x, fmt)
             }
             )*
@@ -653,21 +655,22 @@ uniform_fn_call_workaround! {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::fmt;
 /// use std::io;
 ///
 /// let w = &mut io::stdout() as &mut io::Writer;
-/// format_args!(|args| { fmt::write(w, args) }, "Hello, {}!", "world");
+/// format_args!(|args| { fmt::write(w, args); }, "Hello, {}!", "world");
 /// ```
-pub fn write(output: &mut io::Writer, args: &Arguments) {
+pub fn write(output: &mut io::Writer, args: &Arguments) -> Result {
     unsafe { write_unsafe(output, args.fmt, args.args) }
 }
 
 /// The `writeln` function takes the same arguments as `write`, except that it
 /// will also write a newline (`\n`) character at the end of the format string.
-pub fn writeln(output: &mut io::Writer, args: &Arguments) {
-    unsafe { write_unsafe(output, args.fmt, args.args) }
-    output.write(['\n' as u8]);
+pub fn writeln(output: &mut io::Writer, args: &Arguments) -> Result {
+    let first = unsafe { write_unsafe(output, args.fmt, args.args) };
+    first.and_then(|()| output.write(['\n' as u8]))
 }
 
 /// The `write_unsafe` function takes an output stream, a precompiled format
@@ -692,7 +695,7 @@ pub fn writeln(output: &mut io::Writer, args: &Arguments) {
 /// format string.
 pub unsafe fn write_unsafe(output: &mut io::Writer,
                            fmt: &[rt::Piece],
-                           args: &[Argument]) {
+                           args: &[Argument]) -> Result {
     let mut formatter = Formatter {
         flags: 0,
         width: None,
@@ -704,8 +707,9 @@ pub unsafe fn write_unsafe(output: &mut io::Writer,
         curarg: args.iter(),
     };
     for piece in fmt.iter() {
-        formatter.run(piece, None);
+        if_ok!(formatter.run(piece, None));
     }
+    Ok(())
 }
 
 /// The format function takes a precompiled format string and a list of
@@ -752,7 +756,7 @@ pub fn format(args: &Arguments) -> ~str {
 /// format string.
 pub unsafe fn format_unsafe(fmt: &[rt::Piece], args: &[Argument]) -> ~str {
     let mut output = MemWriter::new();
-    write_unsafe(&mut output as &mut io::Writer, fmt, args);
+    write_unsafe(&mut output as &mut io::Writer, fmt, args).unwrap();
     return str::from_utf8_owned(output.unwrap()).unwrap();
 }
 
@@ -762,10 +766,10 @@ impl<'a> Formatter<'a> {
     // at runtime. This consumes all of the compile-time statics generated by
     // the format! syntax extension.
 
-    fn run(&mut self, piece: &rt::Piece, cur: Option<&str>) {
+    fn run(&mut self, piece: &rt::Piece, cur: Option<&str>) -> Result {
         match *piece {
-            rt::String(s) => { self.buf.write(s.as_bytes()); }
-            rt::CurrentArgument(()) => { self.buf.write(cur.unwrap().as_bytes()); }
+            rt::String(s) => self.buf.write(s.as_bytes()),
+            rt::CurrentArgument(()) => self.buf.write(cur.unwrap().as_bytes()),
             rt::Argument(ref arg) => {
                 // Fill in the format parameters into the formatter
                 self.fill = arg.format.fill;
@@ -782,8 +786,8 @@ impl<'a> Formatter<'a> {
 
                 // Then actually do some printing
                 match arg.method {
-                    None => { (value.formatter)(value.value, self); }
-                    Some(ref method) => { self.execute(*method, value); }
+                    None => (value.formatter)(value.value, self),
+                    Some(ref method) => self.execute(*method, value)
                 }
             }
         }
@@ -804,7 +808,7 @@ impl<'a> Formatter<'a> {
         }
     }
 
-    fn execute(&mut self, method: &rt::Method, arg: Argument) {
+    fn execute(&mut self, method: &rt::Method, arg: Argument) -> Result {
         match *method {
             // Pluralization is selection upon a numeric value specified as the
             // parameter.
@@ -847,7 +851,7 @@ impl<'a> Formatter<'a> {
                     }
                 }
 
-                self.runplural(value, *default);
+                self.runplural(value, *default)
             }
 
             // Select is just a matching against the string specified.
@@ -860,24 +864,26 @@ impl<'a> Formatter<'a> {
                 for s in selectors.iter() {
                     if s.selector == value {
                         for piece in s.result.iter() {
-                            self.run(piece, Some(value));
+                            if_ok!(self.run(piece, Some(value)));
                         }
-                        return;
+                        return Ok(());
                     }
                 }
                 for piece in default.iter() {
-                    self.run(piece, Some(value));
+                    if_ok!(self.run(piece, Some(value)));
                 }
+                Ok(())
             }
         }
     }
 
-    fn runplural(&mut self, value: uint, pieces: &[rt::Piece]) {
+    fn runplural(&mut self, value: uint, pieces: &[rt::Piece]) -> Result {
         ::uint::to_str_bytes(value, 10, |buf| {
             let valuestr = str::from_utf8(buf).unwrap();
             for piece in pieces.iter() {
-                self.run(piece, Some(valuestr));
+                if_ok!(self.run(piece, Some(valuestr)));
             }
+            Ok(())
         })
     }
 
@@ -899,7 +905,7 @@ impl<'a> Formatter<'a> {
     /// This function will correctly account for the flags provided as well as
     /// the minimum width. It will not take precision into account.
     pub fn pad_integral(&mut self, s: &[u8], alternate_prefix: &str,
-                        positive: bool) {
+                        positive: bool) -> Result {
         use fmt::parse::{FlagAlternate, FlagSignPlus, FlagSignAwareZeroPad};
 
         let mut actual_len = s.len();
@@ -916,32 +922,32 @@ impl<'a> Formatter<'a> {
         let sign = |this: &mut Formatter| {
             if !signprinted {
                 if this.flags & 1 << (FlagSignPlus as uint) != 0 && positive {
-                    this.buf.write(['+' as u8]);
+                    if_ok!(this.buf.write(['+' as u8]));
                 } else if !positive {
-                    this.buf.write(['-' as u8]);
+                    if_ok!(this.buf.write(['-' as u8]));
                 }
                 if this.flags & 1 << (FlagAlternate as uint) != 0 {
-                    this.buf.write(alternate_prefix.as_bytes());
+                    if_ok!(this.buf.write(alternate_prefix.as_bytes()));
                 }
                 signprinted = true;
             }
+            Ok(())
         };
 
         let emit = |this: &mut Formatter| {
-            sign(this);
-            this.buf.write(s);
+            sign(this).and_then(|()| this.buf.write(s))
         };
 
         match self.width {
-            None => { emit(self) }
-            Some(min) if actual_len >= min => { emit(self) }
+            None => emit(self),
+            Some(min) if actual_len >= min => emit(self),
             Some(min) => {
                 if self.flags & 1 << (FlagSignAwareZeroPad as uint) != 0 {
                     self.fill = '0';
-                    sign(self);
+                    if_ok!(sign(self));
                 }
                 self.with_padding(min - actual_len, parse::AlignRight, |me| {
-                    emit(me);
+                    emit(me)
                 })
             }
         }
@@ -958,11 +964,10 @@ impl<'a> Formatter<'a> {
     ///               is longer than this length
     ///
     /// Notably this function ignored the `flag` parameters
-    pub fn pad(&mut self, s: &str) {
+    pub fn pad(&mut self, s: &str) -> Result {
         // Make sure there's a fast path up front
         if self.width.is_none() && self.precision.is_none() {
-            self.buf.write(s.as_bytes());
-            return
+            return self.buf.write(s.as_bytes());
         }
         // The `precision` field can be interpreted as a `max-width` for the
         // string being formatted
@@ -974,8 +979,7 @@ impl<'a> Formatter<'a> {
                 let char_len = s.char_len();
                 if char_len >= max {
                     let nchars = ::cmp::min(max, char_len);
-                    self.buf.write(s.slice_chars(0, nchars).as_bytes());
-                    return
+                    return self.buf.write(s.slice_chars(0, nchars).as_bytes());
                 }
             }
             None => {}
@@ -985,7 +989,7 @@ impl<'a> Formatter<'a> {
         match self.width {
             // If we're under the maximum length, and there's no minimum length
             // requirements, then we can just emit the string
-            None => { self.buf.write(s.as_bytes()) }
+            None => self.buf.write(s.as_bytes()),
 
             // If we're under the maximum width, check if we're over the minimum
             // width, if so it's as easy as just emitting the string.
@@ -997,7 +1001,7 @@ impl<'a> Formatter<'a> {
             // up the minimum width with the specified string + some alignment.
             Some(width) => {
                 self.with_padding(width - s.len(), parse::AlignLeft, |me| {
-                    me.buf.write(s.as_bytes());
+                    me.buf.write(s.as_bytes())
                 })
             }
         }
@@ -1006,29 +1010,30 @@ impl<'a> Formatter<'a> {
     fn with_padding(&mut self,
                     padding: uint,
                     default: parse::Alignment,
-                    f: |&mut Formatter|) {
+                    f: |&mut Formatter| -> Result) -> Result {
         let align = match self.align {
             parse::AlignUnknown => default,
             parse::AlignLeft | parse::AlignRight => self.align
         };
         if align == parse::AlignLeft {
-            f(self);
+            if_ok!(f(self));
         }
         let mut fill = [0u8, ..4];
         let len = self.fill.encode_utf8(fill);
         for _ in range(0, padding) {
-            self.buf.write(fill.slice_to(len));
+            if_ok!(self.buf.write(fill.slice_to(len)));
         }
         if align == parse::AlignRight {
-            f(self);
+            if_ok!(f(self));
         }
+        Ok(())
     }
 }
 
 /// This is a function which calls are emitted to by the compiler itself to
 /// create the Argument structures that are passed into the `format` function.
 #[doc(hidden)] #[inline]
-pub fn argument<'a, T>(f: extern "Rust" fn(&T, &mut Formatter),
+pub fn argument<'a, T>(f: extern "Rust" fn(&T, &mut Formatter) -> Result,
                        t: &'a T) -> Argument<'a> {
     unsafe {
         Argument {
@@ -1055,41 +1060,41 @@ pub fn argumentuint<'a>(s: &'a uint) -> Argument<'a> {
 // Implementations of the core formatting traits
 
 impl Bool for bool {
-    fn fmt(b: &bool, f: &mut Formatter) {
-        String::fmt(&(if *b {"true"} else {"false"}), f);
+    fn fmt(b: &bool, f: &mut Formatter) -> Result {
+        String::fmt(&(if *b {"true"} else {"false"}), f)
     }
 }
 
 impl<'a, T: str::Str> String for T {
-    fn fmt(s: &T, f: &mut Formatter) {
-        f.pad(s.as_slice());
+    fn fmt(s: &T, f: &mut Formatter) -> Result {
+        f.pad(s.as_slice())
     }
 }
 
 impl Char for char {
-    fn fmt(c: &char, f: &mut Formatter) {
+    fn fmt(c: &char, f: &mut Formatter) -> Result {
         let mut utf8 = [0u8, ..4];
         let amt = c.encode_utf8(utf8);
         let s: &str = unsafe { cast::transmute(utf8.slice_to(amt)) };
-        String::fmt(&s, f);
+        String::fmt(&s, f)
     }
 }
 
 macro_rules! int_base(($ty:ident, $into:ident, $base:expr,
                        $name:ident, $prefix:expr) => {
     impl $name for $ty {
-        fn fmt(c: &$ty, f: &mut Formatter) {
+        fn fmt(c: &$ty, f: &mut Formatter) -> Result {
             ::$into::to_str_bytes(*c as $into, $base, |buf| {
-                f.pad_integral(buf, $prefix, true);
+                f.pad_integral(buf, $prefix, true)
             })
         }
     }
 })
 macro_rules! upper_hex(($ty:ident, $into:ident) => {
     impl UpperHex for $ty {
-        fn fmt(c: &$ty, f: &mut Formatter) {
+        fn fmt(c: &$ty, f: &mut Formatter) -> Result {
             ::$into::to_str_bytes(*c as $into, 16, |buf| {
-                upperhex(buf, f);
+                upperhex(buf, f)
             })
         }
     }
@@ -1097,7 +1102,7 @@ macro_rules! upper_hex(($ty:ident, $into:ident) => {
 // Not sure why, but this causes an "unresolved enum variant, struct or const"
 // when inlined into the above macro...
 #[doc(hidden)]
-pub fn upperhex(buf: &[u8], f: &mut Formatter) {
+pub fn upperhex(buf: &[u8], f: &mut Formatter) -> Result {
     let mut local = [0u8, ..16];
     for i in ::iter::range(0, buf.len()) {
         local[i] = match buf[i] as char {
@@ -1105,16 +1110,16 @@ pub fn upperhex(buf: &[u8], f: &mut Formatter) {
             c => c as u8,
         }
     }
-    f.pad_integral(local.slice_to(buf.len()), "0x", true);
+    f.pad_integral(local.slice_to(buf.len()), "0x", true)
 }
 
 macro_rules! integer(($signed:ident, $unsigned:ident) => {
     // Signed is special because it actuall emits the negative sign,
     // nothing else should do that, however.
     impl Signed for $signed {
-        fn fmt(c: &$signed, f: &mut Formatter) {
+        fn fmt(c: &$signed, f: &mut Formatter) -> Result {
             ::$unsigned::to_str_bytes(c.abs() as $unsigned, 10, |buf| {
-                f.pad_integral(buf, "", *c >= 0);
+                f.pad_integral(buf, "", *c >= 0)
             })
         }
     }
@@ -1138,35 +1143,35 @@ integer!(i64, u64)
 
 macro_rules! floating(($ty:ident) => {
     impl Float for $ty {
-        fn fmt(f: &$ty, fmt: &mut Formatter) {
+        fn fmt(f: &$ty, fmt: &mut Formatter) -> Result {
             // FIXME: this shouldn't perform an allocation
             let s = match fmt.precision {
                 Some(i) => ::$ty::to_str_exact(f.abs(), i),
                 None => ::$ty::to_str_digits(f.abs(), 6)
             };
-            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0);
+            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0)
         }
     }
 
     impl LowerExp for $ty {
-        fn fmt(f: &$ty, fmt: &mut Formatter) {
+        fn fmt(f: &$ty, fmt: &mut Formatter) -> Result {
             // FIXME: this shouldn't perform an allocation
             let s = match fmt.precision {
                 Some(i) => ::$ty::to_str_exp_exact(f.abs(), i, false),
                 None => ::$ty::to_str_exp_digits(f.abs(), 6, false)
             };
-            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0);
+            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0)
         }
     }
 
     impl UpperExp for $ty {
-        fn fmt(f: &$ty, fmt: &mut Formatter) {
+        fn fmt(f: &$ty, fmt: &mut Formatter) -> Result {
             // FIXME: this shouldn't perform an allocation
             let s = match fmt.precision {
                 Some(i) => ::$ty::to_str_exp_exact(f.abs(), i, true),
                 None => ::$ty::to_str_exp_digits(f.abs(), 6, true)
             };
-            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0);
+            fmt.pad_integral(s.as_bytes(), "", *f >= 0.0)
         }
     }
 })
@@ -1174,39 +1179,41 @@ floating!(f32)
 floating!(f64)
 
 impl<T> Poly for T {
-    fn fmt(t: &T, f: &mut Formatter) {
+    fn fmt(t: &T, f: &mut Formatter) -> Result {
         match (f.width, f.precision) {
             (None, None) => {
-                repr::write_repr(f.buf, t);
+                repr::write_repr(f.buf, t)
             }
 
             // If we have a specified width for formatting, then we have to make
             // this allocation of a new string
             _ => {
                 let s = repr::repr_to_str(t);
-                f.pad(s);
+                f.pad(s)
             }
         }
     }
 }
 
 impl<T> Pointer for *T {
-    fn fmt(t: &*T, f: &mut Formatter) {
+    fn fmt(t: &*T, f: &mut Formatter) -> Result {
         f.flags |= 1 << (parse::FlagAlternate as uint);
         ::uint::to_str_bytes(*t as uint, 16, |buf| {
-            f.pad_integral(buf, "0x", true);
+            f.pad_integral(buf, "0x", true)
         })
     }
 }
 impl<T> Pointer for *mut T {
-    fn fmt(t: &*mut T, f: &mut Formatter) { Pointer::fmt(&(*t as *T), f) }
+    fn fmt(t: &*mut T, f: &mut Formatter) -> Result {
+        Pointer::fmt(&(*t as *T), f)
+    }
 }
 
 // Implementation of Show for various core types
 
 macro_rules! delegate(($ty:ty to $other:ident) => {
     impl<'a> Show for $ty {
-        fn fmt(me: &$ty, f: &mut Formatter) {
+        fn fmt(me: &$ty, f: &mut Formatter) -> Result {
             $other::fmt(me, f)
         }
     }
@@ -1229,10 +1236,10 @@ delegate!(f32 to Float)
 delegate!(f64 to Float)
 
 impl<T> Show for *T {
-    fn fmt(me: &*T, f: &mut Formatter) { Pointer::fmt(me, f) }
+    fn fmt(me: &*T, f: &mut Formatter) -> Result { Pointer::fmt(me, f) }
 }
 impl<T> Show for *mut T {
-    fn fmt(me: &*mut T, f: &mut Formatter) { Pointer::fmt(me, f) }
+    fn fmt(me: &*mut T, f: &mut Formatter) -> Result { Pointer::fmt(me, f) }
 }
 
 // If you expected tests to be here, look instead at the run-pass/ifmt.rs test,
diff --git a/src/libstd/hash.rs b/src/libstd/hash.rs
index 1444f9b4129..4163d1e0c96 100644
--- a/src/libstd/hash.rs
+++ b/src/libstd/hash.rs
@@ -27,13 +27,14 @@
 #[allow(missing_doc)];
 
 use container::Container;
+use io::{Writer, IoResult};
 use iter::Iterator;
+use num::ToStrRadix;
 use option::{Some, None};
-use io::Writer;
+use result::Ok;
 use str::OwnedStr;
 use to_bytes::IterBytes;
 use vec::ImmutableVector;
-use num::ToStrRadix;
 
 // Alias `SipState` to `State`.
 pub use State = hash::SipState;
@@ -164,7 +165,7 @@ macro_rules! compress (
 impl Writer for SipState {
     // Methods for io::writer
     #[inline]
-    fn write(&mut self, msg: &[u8]) {
+    fn write(&mut self, msg: &[u8]) -> IoResult<()> {
         let length = msg.len();
         self.length += length;
 
@@ -180,7 +181,7 @@ impl Writer for SipState {
                     t += 1;
                 }
                 self.ntail += length;
-                return;
+                return Ok(())
             }
 
             let mut t = 0;
@@ -222,17 +223,14 @@ impl Writer for SipState {
             t += 1
         }
         self.ntail = left;
-    }
-
-    fn flush(&mut self) {
-        // No-op
+        Ok(())
     }
 }
 
 impl Streaming for SipState {
     #[inline]
     fn input(&mut self, buf: &[u8]) {
-        self.write(buf);
+        self.write(buf).unwrap();
     }
 
     #[inline]
diff --git a/src/libstd/io/buffered.rs b/src/libstd/io/buffered.rs
index 64e42c5480f..256f9d325f3 100644
--- a/src/libstd/io/buffered.rs
+++ b/src/libstd/io/buffered.rs
@@ -11,10 +11,11 @@
 //! Buffering wrappers for I/O traits
 
 use container::Container;
-use io::{Reader, Writer, Stream, Buffer, DEFAULT_BUF_SIZE};
+use io::{Reader, Writer, Stream, Buffer, DEFAULT_BUF_SIZE, IoResult};
 use iter::ExactSize;
 use num;
-use option::{Option, Some, None};
+use option::{Some, None};
+use result::{Ok, Err};
 use vec::{OwnedVector, ImmutableVector, MutableVector};
 use vec;
 
@@ -30,14 +31,13 @@ use vec;
 /// ```rust
 /// use std::io::{BufferedReader, File};
 ///
-/// # let _g = ::std::io::ignore_io_error();
 /// let file = File::open(&Path::new("message.txt"));
 /// let mut reader = BufferedReader::new(file);
 ///
 /// let mut buf = [0, ..100];
 /// match reader.read(buf) {
-///     Some(nread) => println!("Read {} bytes", nread),
-///     None => println!("At the end of the file!")
+///     Ok(nread) => println!("Read {} bytes", nread),
+///     Err(e) => println!("error reading: {}", e)
 /// }
 /// ```
 pub struct BufferedReader<R> {
@@ -86,17 +86,12 @@ impl<R: Reader> BufferedReader<R> {
 }
 
 impl<R: Reader> Buffer for BufferedReader<R> {
-    fn fill<'a>(&'a mut self) -> &'a [u8] {
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> {
         if self.pos == self.cap {
-            match self.inner.read(self.buf) {
-                Some(cap) => {
-                    self.pos = 0;
-                    self.cap = cap;
-                }
-                None => { self.eof = true; }
-            }
+            self.cap = if_ok!(self.inner.read(self.buf));
+            self.pos = 0;
         }
-        return self.buf.slice(self.pos, self.cap);
+        Ok(self.buf.slice(self.pos, self.cap))
     }
 
     fn consume(&mut self, amt: uint) {
@@ -106,18 +101,15 @@ impl<R: Reader> Buffer for BufferedReader<R> {
 }
 
 impl<R: Reader> Reader for BufferedReader<R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let nread = {
-            let available = self.fill();
+            let available = if_ok!(self.fill());
             let nread = num::min(available.len(), buf.len());
             vec::bytes::copy_memory(buf, available.slice_to(nread));
             nread
         };
         self.pos += nread;
-        if nread == 0 && buf.len() != 0 && self.eof {
-            return None;
-        }
-        Some(nread)
+        Ok(nread)
     }
 }
 
@@ -128,9 +120,9 @@ impl<R: Reader> Reader for BufferedReader<R> {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::{BufferedWriter, File};
 ///
-/// # let _g = ::std::io::ignore_io_error();
 /// let file = File::open(&Path::new("message.txt"));
 /// let mut writer = BufferedWriter::new(file);
 ///
@@ -161,10 +153,13 @@ impl<W: Writer> BufferedWriter<W> {
         BufferedWriter::with_capacity(DEFAULT_BUF_SIZE, inner)
     }
 
-    fn flush_buf(&mut self) {
+    fn flush_buf(&mut self) -> IoResult<()> {
         if self.pos != 0 {
-            self.inner.write(self.buf.slice_to(self.pos));
+            let ret = self.inner.write(self.buf.slice_to(self.pos));
             self.pos = 0;
+            ret
+        } else {
+            Ok(())
         }
     }
 
@@ -178,29 +173,30 @@ impl<W: Writer> BufferedWriter<W> {
     ///
     /// The buffer is flushed before returning the writer.
     pub fn unwrap(mut self) -> W {
-        self.flush_buf();
+        // FIXME: is failing the right thing to do if flushing fails?
+        self.flush_buf().unwrap();
         self.inner
     }
 }
 
 impl<W: Writer> Writer for BufferedWriter<W> {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         if self.pos + buf.len() > self.buf.len() {
-            self.flush_buf();
+            if_ok!(self.flush_buf());
         }
 
         if buf.len() > self.buf.len() {
-            self.inner.write(buf);
+            self.inner.write(buf)
         } else {
             let dst = self.buf.mut_slice_from(self.pos);
             vec::bytes::copy_memory(dst, buf);
             self.pos += buf.len();
+            Ok(())
         }
     }
 
-    fn flush(&mut self) {
-        self.flush_buf();
-        self.inner.flush();
+    fn flush(&mut self) -> IoResult<()> {
+        self.flush_buf().and_then(|()| self.inner.flush())
     }
 }
 
@@ -234,18 +230,19 @@ impl<W: Writer> LineBufferedWriter<W> {
 }
 
 impl<W: Writer> Writer for LineBufferedWriter<W> {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         match buf.iter().rposition(|&b| b == '\n' as u8) {
             Some(i) => {
-                self.inner.write(buf.slice_to(i + 1));
-                self.inner.flush();
-                self.inner.write(buf.slice_from(i + 1));
+                if_ok!(self.inner.write(buf.slice_to(i + 1)));
+                if_ok!(self.inner.flush());
+                if_ok!(self.inner.write(buf.slice_from(i + 1)));
+                Ok(())
             }
             None => self.inner.write(buf),
         }
     }
 
-    fn flush(&mut self) { self.inner.flush() }
+    fn flush(&mut self) -> IoResult<()> { self.inner.flush() }
 }
 
 struct InternalBufferedWriter<W>(BufferedWriter<W>);
@@ -258,7 +255,9 @@ impl<W> InternalBufferedWriter<W> {
 }
 
 impl<W: Reader> Reader for InternalBufferedWriter<W> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.get_mut_ref().inner.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        self.get_mut_ref().inner.read(buf)
+    }
 }
 
 /// Wraps a Stream and buffers input and output to and from it
@@ -268,9 +267,9 @@ impl<W: Reader> Reader for InternalBufferedWriter<W> {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::{BufferedStream, File};
 ///
-/// # let _g = ::std::io::ignore_io_error();
 /// let file = File::open(&Path::new("message.txt"));
 /// let mut stream = BufferedStream::new(file);
 ///
@@ -279,8 +278,8 @@ impl<W: Reader> Reader for InternalBufferedWriter<W> {
 ///
 /// let mut buf = [0, ..100];
 /// match stream.read(buf) {
-///     Some(nread) => println!("Read {} bytes", nread),
-///     None => println!("At the end of the stream!")
+///     Ok(nread) => println!("Read {} bytes", nread),
+///     Err(e) => println!("error reading: {}", e)
 /// }
 /// ```
 pub struct BufferedStream<S> {
@@ -326,17 +325,23 @@ impl<S: Stream> BufferedStream<S> {
 }
 
 impl<S: Stream> Buffer for BufferedStream<S> {
-    fn fill<'a>(&'a mut self) -> &'a [u8] { self.inner.fill() }
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> { self.inner.fill() }
     fn consume(&mut self, amt: uint) { self.inner.consume(amt) }
 }
 
 impl<S: Stream> Reader for BufferedStream<S> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.inner.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        self.inner.read(buf)
+    }
 }
 
 impl<S: Stream> Writer for BufferedStream<S> {
-    fn write(&mut self, buf: &[u8]) { self.inner.inner.get_mut_ref().write(buf) }
-    fn flush(&mut self) { self.inner.inner.get_mut_ref().flush() }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        self.inner.inner.get_mut_ref().write(buf)
+    }
+    fn flush(&mut self) -> IoResult<()> {
+        self.inner.inner.get_mut_ref().flush()
+    }
 }
 
 #[cfg(test)]
@@ -354,13 +359,13 @@ mod test {
     pub struct NullStream;
 
     impl Reader for NullStream {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            None
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            Err(io::standard_error(io::EndOfFile))
         }
     }
 
     impl Writer for NullStream {
-        fn write(&mut self, _: &[u8]) { }
+        fn write(&mut self, _: &[u8]) -> io::IoResult<()> { Ok(()) }
     }
 
     /// A dummy reader intended at testing short-reads propagation.
@@ -369,8 +374,11 @@ mod test {
     }
 
     impl Reader for ShortReader {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            self.lengths.shift()
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            match self.lengths.shift() {
+                Some(i) => Ok(i),
+                None => Err(io::standard_error(io::EndOfFile))
+            }
         }
     }
 
@@ -381,24 +389,24 @@ mod test {
 
         let mut buf = [0, 0, 0];
         let nread = reader.read(buf);
-        assert_eq!(Some(2), nread);
+        assert_eq!(Ok(2), nread);
         assert_eq!([0, 1, 0], buf);
 
         let mut buf = [0];
         let nread = reader.read(buf);
-        assert_eq!(Some(1), nread);
+        assert_eq!(Ok(1), nread);
         assert_eq!([2], buf);
 
         let mut buf = [0, 0, 0];
         let nread = reader.read(buf);
-        assert_eq!(Some(1), nread);
+        assert_eq!(Ok(1), nread);
         assert_eq!([3, 0, 0], buf);
 
         let nread = reader.read(buf);
-        assert_eq!(Some(1), nread);
+        assert_eq!(Ok(1), nread);
         assert_eq!([4, 0, 0], buf);
 
-        assert_eq!(None, reader.read(buf));
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
@@ -406,35 +414,35 @@ mod test {
         let inner = MemWriter::new();
         let mut writer = BufferedWriter::with_capacity(2, inner);
 
-        writer.write([0, 1]);
+        writer.write([0, 1]).unwrap();
         assert_eq!([], writer.get_ref().get_ref());
 
-        writer.write([2]);
+        writer.write([2]).unwrap();
         assert_eq!([0, 1], writer.get_ref().get_ref());
 
-        writer.write([3]);
+        writer.write([3]).unwrap();
         assert_eq!([0, 1], writer.get_ref().get_ref());
 
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!([0, 1, 2, 3], writer.get_ref().get_ref());
 
-        writer.write([4]);
-        writer.write([5]);
+        writer.write([4]).unwrap();
+        writer.write([5]).unwrap();
         assert_eq!([0, 1, 2, 3], writer.get_ref().get_ref());
 
-        writer.write([6]);
+        writer.write([6]).unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5],
                    writer.get_ref().get_ref());
 
-        writer.write([7, 8]);
+        writer.write([7, 8]).unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5, 6],
                    writer.get_ref().get_ref());
 
-        writer.write([9, 10, 11]);
+        writer.write([9, 10, 11]).unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
                    writer.get_ref().get_ref());
 
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
                    writer.get_ref().get_ref());
     }
@@ -442,7 +450,7 @@ mod test {
     #[test]
     fn test_buffered_writer_inner_flushes() {
         let mut w = BufferedWriter::with_capacity(3, MemWriter::new());
-        w.write([0, 1]);
+        w.write([0, 1]).unwrap();
         assert_eq!([], w.get_ref().get_ref());
         let w = w.unwrap();
         assert_eq!([0, 1], w.get_ref());
@@ -455,47 +463,49 @@ mod test {
         struct S;
 
         impl io::Writer for S {
-            fn write(&mut self, _: &[u8]) {}
+            fn write(&mut self, _: &[u8]) -> io::IoResult<()> { Ok(()) }
         }
 
         impl io::Reader for S {
-            fn read(&mut self, _: &mut [u8]) -> Option<uint> { None }
+            fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+                Err(io::standard_error(io::EndOfFile))
+            }
         }
 
         let mut stream = BufferedStream::new(S);
         let mut buf = [];
-        stream.read(buf);
-        stream.write(buf);
-        stream.flush();
+        assert!(stream.read(buf).is_err());
+        stream.write(buf).unwrap();
+        stream.flush().unwrap();
     }
 
     #[test]
     fn test_read_until() {
         let inner = MemReader::new(~[0, 1, 2, 1, 0]);
         let mut reader = BufferedReader::with_capacity(2, inner);
-        assert_eq!(reader.read_until(0), Some(~[0]));
-        assert_eq!(reader.read_until(2), Some(~[1, 2]));
-        assert_eq!(reader.read_until(1), Some(~[1]));
-        assert_eq!(reader.read_until(8), Some(~[0]));
-        assert_eq!(reader.read_until(9), None);
+        assert_eq!(reader.read_until(0), Ok(~[0]));
+        assert_eq!(reader.read_until(2), Ok(~[1, 2]));
+        assert_eq!(reader.read_until(1), Ok(~[1]));
+        assert_eq!(reader.read_until(8), Ok(~[0]));
+        assert!(reader.read_until(9).is_err());
     }
 
     #[test]
     fn test_line_buffer() {
         let mut writer = LineBufferedWriter::new(MemWriter::new());
-        writer.write([0]);
+        writer.write([0]).unwrap();
         assert_eq!(writer.get_ref().get_ref(), []);
-        writer.write([1]);
+        writer.write([1]).unwrap();
         assert_eq!(writer.get_ref().get_ref(), []);
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!(writer.get_ref().get_ref(), [0, 1]);
-        writer.write([0, '\n' as u8, 1, '\n' as u8, 2]);
+        writer.write([0, '\n' as u8, 1, '\n' as u8, 2]).unwrap();
         assert_eq!(writer.get_ref().get_ref(),
             [0, 1, 0, '\n' as u8, 1, '\n' as u8]);
-        writer.flush();
+        writer.flush().unwrap();
         assert_eq!(writer.get_ref().get_ref(),
             [0, 1, 0, '\n' as u8, 1, '\n' as u8, 2]);
-        writer.write([3, '\n' as u8]);
+        writer.write([3, '\n' as u8]).unwrap();
         assert_eq!(writer.get_ref().get_ref(),
             [0, 1, 0, '\n' as u8, 1, '\n' as u8, 2, 3, '\n' as u8]);
     }
@@ -504,10 +514,10 @@ mod test {
     fn test_read_line() {
         let in_buf = MemReader::new(bytes!("a\nb\nc").to_owned());
         let mut reader = BufferedReader::with_capacity(2, in_buf);
-        assert_eq!(reader.read_line(), Some(~"a\n"));
-        assert_eq!(reader.read_line(), Some(~"b\n"));
-        assert_eq!(reader.read_line(), Some(~"c"));
-        assert_eq!(reader.read_line(), None);
+        assert_eq!(reader.read_line(), Ok(~"a\n"));
+        assert_eq!(reader.read_line(), Ok(~"b\n"));
+        assert_eq!(reader.read_line(), Ok(~"c"));
+        assert!(reader.read_line().is_err());
     }
 
     #[test]
@@ -526,20 +536,20 @@ mod test {
         let inner = ShortReader{lengths: ~[0, 1, 2, 0, 1, 0]};
         let mut reader = BufferedReader::new(inner);
         let mut buf = [0, 0];
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.read(buf), Some(2));
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.read(buf), None);
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.read(buf), Ok(2));
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.read(buf), Ok(0));
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
     fn read_char_buffered() {
         let buf = [195u8, 159u8];
         let mut reader = BufferedReader::with_capacity(1, BufReader::new(buf));
-        assert_eq!(reader.read_char(), Some('ß'));
+        assert_eq!(reader.read_char(), Ok('ß'));
     }
 
     #[bench]
diff --git a/src/libstd/io/comm_adapters.rs b/src/libstd/io/comm_adapters.rs
index 1eaa752d2a3..6ed588ac69f 100644
--- a/src/libstd/io/comm_adapters.rs
+++ b/src/libstd/io/comm_adapters.rs
@@ -14,7 +14,7 @@ use comm::{Port, Chan};
 use cmp;
 use io;
 use option::{None, Option, Some};
-use super::{Reader, Writer};
+use super::{Reader, Writer, IoResult};
 use vec::{bytes, CloneableVector, MutableVector, ImmutableVector};
 
 /// Allows reading from a port.
@@ -49,7 +49,7 @@ impl PortReader {
 }
 
 impl Reader for PortReader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let mut num_read = 0;
         loop {
             match self.buf {
@@ -71,10 +71,9 @@ impl Reader for PortReader {
             self.closed = self.buf.is_none();
         }
         if self.closed && num_read == 0 {
-            io::io_error::cond.raise(io::standard_error(io::EndOfFile));
-            None
+            Err(io::standard_error(io::EndOfFile))
         } else {
-            Some(num_read)
+            Ok(num_read)
         }
     }
 }
@@ -98,13 +97,15 @@ impl ChanWriter {
 }
 
 impl Writer for ChanWriter {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         if !self.chan.try_send(buf.to_owned()) {
-            io::io_error::cond.raise(io::IoError {
+            Err(io::IoError {
                 kind: io::BrokenPipe,
                 desc: "Pipe closed",
                 detail: None
-            });
+            })
+        } else {
+            Ok(())
         }
     }
 }
@@ -132,36 +133,28 @@ mod test {
         let mut buf = ~[0u8, ..3];
 
 
-        assert_eq!(Some(0), reader.read([]));
+        assert_eq!(Ok(0), reader.read([]));
 
-        assert_eq!(Some(3), reader.read(buf));
+        assert_eq!(Ok(3), reader.read(buf));
         assert_eq!(~[1,2,3], buf);
 
-        assert_eq!(Some(3), reader.read(buf));
+        assert_eq!(Ok(3), reader.read(buf));
         assert_eq!(~[4,5,6], buf);
 
-        assert_eq!(Some(2), reader.read(buf));
+        assert_eq!(Ok(2), reader.read(buf));
         assert_eq!(~[7,8,6], buf);
 
-        let mut err = None;
-        let result = io::io_error::cond.trap(|io::standard_error(k, _, _)| {
-            err = Some(k)
-        }).inside(|| {
-            reader.read(buf)
-        });
-        assert_eq!(Some(io::EndOfFile), err);
-        assert_eq!(None, result);
+        match reader.read(buf) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
         assert_eq!(~[7,8,6], buf);
 
         // Ensure it continues to fail in the same way.
-        err = None;
-        let result = io::io_error::cond.trap(|io::standard_error(k, _, _)| {
-            err = Some(k)
-        }).inside(|| {
-            reader.read(buf)
-        });
-        assert_eq!(Some(io::EndOfFile), err);
-        assert_eq!(None, result);
+        match reader.read(buf) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
         assert_eq!(~[7,8,6], buf);
     }
 
@@ -169,18 +162,15 @@ mod test {
     fn test_chan_writer() {
         let (port, chan) = Chan::new();
         let mut writer = ChanWriter::new(chan);
-        writer.write_be_u32(42);
+        writer.write_be_u32(42).unwrap();
 
         let wanted = ~[0u8, 0u8, 0u8, 42u8];
         let got = task::try(proc() { port.recv() }).unwrap();
         assert_eq!(wanted, got);
 
-        let mut err = None;
-        io::io_error::cond.trap(|io::IoError { kind, .. } | {
-            err = Some(kind)
-        }).inside(|| {
-            writer.write_u8(1)
-        });
-        assert_eq!(Some(io::BrokenPipe), err);
+        match writer.write_u8(1) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::BrokenPipe),
+        }
     }
 }
diff --git a/src/libstd/io/extensions.rs b/src/libstd/io/extensions.rs
index 548dc3efe92..49d51cbb26f 100644
--- a/src/libstd/io/extensions.rs
+++ b/src/libstd/io/extensions.rs
@@ -46,7 +46,7 @@ impl<'r, R: Reader> Bytes<'r, R> {
 impl<'r, R: Reader> Iterator<u8> for Bytes<'r, R> {
     #[inline]
     fn next(&mut self) -> Option<u8> {
-        self.reader.read_byte()
+        self.reader.read_byte().ok()
     }
 }
 
@@ -125,23 +125,22 @@ pub fn u64_from_be_bytes(data: &[u8],
 
 #[cfg(test)]
 mod test {
-    use unstable::finally::Finally;
     use prelude::*;
+    use io;
     use io::{MemReader, MemWriter};
-    use io::{io_error, placeholder_error};
 
     struct InitialZeroByteReader {
         count: int,
     }
 
     impl Reader for InitialZeroByteReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
-                Some(0)
+                Ok(0)
             } else {
                 buf[0] = 10;
-                Some(1)
+                Ok(1)
             }
         }
     }
@@ -149,17 +148,16 @@ mod test {
     struct EofReader;
 
     impl Reader for EofReader {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            None
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            Err(io::standard_error(io::EndOfFile))
         }
     }
 
     struct ErroringReader;
 
     impl Reader for ErroringReader {
-        fn read(&mut self, _: &mut [u8]) -> Option<uint> {
-            io_error::cond.raise(placeholder_error());
-            None
+        fn read(&mut self, _: &mut [u8]) -> io::IoResult<uint> {
+            Err(io::standard_error(io::InvalidInput))
         }
     }
 
@@ -168,16 +166,16 @@ mod test {
     }
 
     impl Reader for PartialReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
                 buf[0] = 10;
                 buf[1] = 11;
-                Some(2)
+                Ok(2)
             } else {
                 buf[0] = 12;
                 buf[1] = 13;
-                Some(2)
+                Ok(2)
             }
         }
     }
@@ -187,14 +185,13 @@ mod test {
     }
 
     impl Reader for ErroringLaterReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
                 buf[0] = 10;
-                Some(1)
+                Ok(1)
             } else {
-                io_error::cond.raise(placeholder_error());
-                None
+                Err(io::standard_error(io::InvalidInput))
             }
         }
     }
@@ -204,19 +201,19 @@ mod test {
     }
 
     impl Reader for ThreeChunkReader {
-        fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+        fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
             if self.count == 0 {
                 self.count = 1;
                 buf[0] = 10;
                 buf[1] = 11;
-                Some(2)
+                Ok(2)
             } else if self.count == 1 {
                 self.count = 2;
                 buf[0] = 12;
                 buf[1] = 13;
-                Some(2)
+                Ok(2)
             } else {
-                None
+                Err(io::standard_error(io::EndOfFile))
             }
         }
     }
@@ -225,7 +222,7 @@ mod test {
     fn read_byte() {
         let mut reader = MemReader::new(~[10]);
         let byte = reader.read_byte();
-        assert!(byte == Some(10));
+        assert!(byte == Ok(10));
     }
 
     #[test]
@@ -234,24 +231,21 @@ mod test {
             count: 0,
         };
         let byte = reader.read_byte();
-        assert!(byte == Some(10));
+        assert!(byte == Ok(10));
     }
 
     #[test]
     fn read_byte_eof() {
         let mut reader = EofReader;
         let byte = reader.read_byte();
-        assert!(byte == None);
+        assert!(byte.is_err());
     }
 
     #[test]
     fn read_byte_error() {
         let mut reader = ErroringReader;
-        io_error::cond.trap(|_| {
-        }).inside(|| {
-            let byte = reader.read_byte();
-            assert!(byte == None);
-        });
+        let byte = reader.read_byte();
+        assert!(byte.is_err());
     }
 
     #[test]
@@ -267,23 +261,21 @@ mod test {
     fn bytes_eof() {
         let mut reader = EofReader;
         let byte = reader.bytes().next();
-        assert!(byte == None);
+        assert!(byte.is_none());
     }
 
     #[test]
     fn bytes_error() {
         let mut reader = ErroringReader;
         let mut it = reader.bytes();
-        io_error::cond.trap(|_| ()).inside(|| {
-            let byte = it.next();
-            assert!(byte == None);
-        })
+        let byte = it.next();
+        assert!(byte.is_none());
     }
 
     #[test]
     fn read_bytes() {
         let mut reader = MemReader::new(~[10, 11, 12, 13]);
-        let bytes = reader.read_bytes(4);
+        let bytes = reader.read_bytes(4).unwrap();
         assert!(bytes == ~[10, 11, 12, 13]);
     }
 
@@ -292,24 +284,21 @@ mod test {
         let mut reader = PartialReader {
             count: 0,
         };
-        let bytes = reader.read_bytes(4);
+        let bytes = reader.read_bytes(4).unwrap();
         assert!(bytes == ~[10, 11, 12, 13]);
     }
 
     #[test]
     fn read_bytes_eof() {
         let mut reader = MemReader::new(~[10, 11]);
-        io_error::cond.trap(|_| {
-        }).inside(|| {
-            assert!(reader.read_bytes(4) == ~[10, 11]);
-        })
+        assert!(reader.read_bytes(4).is_err());
     }
 
     #[test]
     fn push_bytes() {
         let mut reader = MemReader::new(~[10, 11, 12, 13]);
         let mut buf = ~[8, 9];
-        reader.push_bytes(&mut buf, 4);
+        reader.push_bytes(&mut buf, 4).unwrap();
         assert!(buf == ~[8, 9, 10, 11, 12, 13]);
     }
 
@@ -319,7 +308,7 @@ mod test {
             count: 0,
         };
         let mut buf = ~[8, 9];
-        reader.push_bytes(&mut buf, 4);
+        reader.push_bytes(&mut buf, 4).unwrap();
         assert!(buf == ~[8, 9, 10, 11, 12, 13]);
     }
 
@@ -327,11 +316,8 @@ mod test {
     fn push_bytes_eof() {
         let mut reader = MemReader::new(~[10, 11]);
         let mut buf = ~[8, 9];
-        io_error::cond.trap(|_| {
-        }).inside(|| {
-            reader.push_bytes(&mut buf, 4);
-            assert!(buf == ~[8, 9, 10, 11]);
-        })
+        assert!(reader.push_bytes(&mut buf, 4).is_err());
+        assert!(buf == ~[8, 9, 10, 11]);
     }
 
     #[test]
@@ -340,38 +326,16 @@ mod test {
             count: 0,
         };
         let mut buf = ~[8, 9];
-        io_error::cond.trap(|_| { } ).inside(|| {
-            reader.push_bytes(&mut buf, 4);
-        });
+        assert!(reader.push_bytes(&mut buf, 4).is_err());
         assert!(buf == ~[8, 9, 10]);
     }
 
     #[test]
-    #[should_fail]
-    #[ignore] // borrow issues with RefCell
-    fn push_bytes_fail_reset_len() {
-        // push_bytes unsafely sets the vector length. This is testing that
-        // upon failure the length is reset correctly.
-        let _reader = ErroringLaterReader {
-            count: 0,
-        };
-        // FIXME (#7049): Figure out some other way to do this.
-        //let buf = RefCell::new(~[8, 9]);
-        (|| {
-            //reader.push_bytes(buf.borrow_mut().get(), 4);
-        }).finally(|| {
-            // NB: Using rtassert here to trigger abort on failure since this is a should_fail test
-            // FIXME: #7049 This fails because buf is still borrowed
-            //rtassert!(buf.borrow().get() == ~[8, 9, 10]);
-        })
-    }
-
-    #[test]
     fn read_to_end() {
         let mut reader = ThreeChunkReader {
             count: 0,
         };
-        let buf = reader.read_to_end();
+        let buf = reader.read_to_end().unwrap();
         assert!(buf == ~[10, 11, 12, 13]);
     }
 
@@ -381,7 +345,7 @@ mod test {
         let mut reader = ThreeChunkReader {
             count: 0,
         };
-        let buf = reader.read_to_end();
+        let buf = reader.read_to_end().unwrap();
         assert!(buf == ~[10, 11]);
     }
 
@@ -391,12 +355,12 @@ mod test {
 
         let mut writer = MemWriter::new();
         for i in uints.iter() {
-            writer.write_le_u64(*i);
+            writer.write_le_u64(*i).unwrap();
         }
 
         let mut reader = MemReader::new(writer.unwrap());
         for i in uints.iter() {
-            assert!(reader.read_le_u64() == *i);
+            assert!(reader.read_le_u64().unwrap() == *i);
         }
     }
 
@@ -407,12 +371,12 @@ mod test {
 
         let mut writer = MemWriter::new();
         for i in uints.iter() {
-            writer.write_be_u64(*i);
+            writer.write_be_u64(*i).unwrap();
         }
 
         let mut reader = MemReader::new(writer.unwrap());
         for i in uints.iter() {
-            assert!(reader.read_be_u64() == *i);
+            assert!(reader.read_be_u64().unwrap() == *i);
         }
     }
 
@@ -422,14 +386,14 @@ mod test {
 
         let mut writer = MemWriter::new();
         for i in ints.iter() {
-            writer.write_be_i32(*i);
+            writer.write_be_i32(*i).unwrap();
         }
 
         let mut reader = MemReader::new(writer.unwrap());
         for i in ints.iter() {
             // this tests that the sign extension is working
             // (comparing the values as i32 would not test this)
-            assert!(reader.read_be_int_n(4) == *i as i64);
+            assert!(reader.read_be_int_n(4).unwrap() == *i as i64);
         }
     }
 
@@ -439,10 +403,10 @@ mod test {
         let buf = ~[0x41, 0x02, 0x00, 0x00];
 
         let mut writer = MemWriter::new();
-        writer.write(buf);
+        writer.write(buf).unwrap();
 
         let mut reader = MemReader::new(writer.unwrap());
-        let f = reader.read_be_f32();
+        let f = reader.read_be_f32().unwrap();
         assert!(f == 8.1250);
     }
 
@@ -451,12 +415,12 @@ mod test {
         let f:f32 = 8.1250;
 
         let mut writer = MemWriter::new();
-        writer.write_be_f32(f);
-        writer.write_le_f32(f);
+        writer.write_be_f32(f).unwrap();
+        writer.write_le_f32(f).unwrap();
 
         let mut reader = MemReader::new(writer.unwrap());
-        assert!(reader.read_be_f32() == 8.1250);
-        assert!(reader.read_le_f32() == 8.1250);
+        assert!(reader.read_be_f32().unwrap() == 8.1250);
+        assert!(reader.read_le_f32().unwrap() == 8.1250);
     }
 
     #[test]
diff --git a/src/libstd/io/fs.rs b/src/libstd/io/fs.rs
index 8904101dd05..ef1b1a56ec0 100644
--- a/src/libstd/io/fs.rs
+++ b/src/libstd/io/fs.rs
@@ -14,11 +14,11 @@ This module provides a set of functions and traits for working
 with regular files & directories on a filesystem.
 
 At the top-level of the module are a set of freestanding functions, associated
-with various filesystem operations. They all operate on a `Path` object.
+with various filesystem operations. They all operate on `Path` objects.
 
 All operations in this module, including those as part of `File` et al
-block the task during execution. Most will raise `std::io::io_error`
-conditions in the event of failure.
+block the task during execution. In the event of failure, all functions/methods
+will return an `IoResult` type with an `Err` value.
 
 Also included in this module is an implementation block on the `Path` object
 defined in `std::path::Path`. The impl adds useful methods about inspecting the
@@ -27,21 +27,25 @@ particular bits of it, etc.
 
 # Example
 
-    use std::io::{File, fs};
+```rust
+# #[allow(unused_must_use)];
+use std::io::{File, fs};
 
-    let path = Path::new("foo.txt");
+let path = Path::new("foo.txt");
 
-    // create the file, whether it exists or not
-    let mut file = File::create(&path);
-    file.write(bytes!("foobar"));
+// create the file, whether it exists or not
+let mut file = File::create(&path);
+file.write(bytes!("foobar"));
+# drop(file);
 
-    // open the file in read-only mode
-    let mut file = File::open(&path);
-    file.read_to_end();
+// open the file in read-only mode
+let mut file = File::open(&path);
+file.read_to_end();
 
-    println!("{}", path.stat().size);
-    fs::symlink(&path, &Path::new("bar.txt"));
-    fs::unlink(&path);
+println!("{}", path.stat().unwrap().size);
+# drop(file);
+fs::unlink(&path);
+```
 
 */
 
@@ -50,7 +54,7 @@ use clone::Clone;
 use iter::Iterator;
 use super::{Reader, Writer, Seek};
 use super::{SeekStyle, Read, Write, Open, IoError, Truncate,
-            FileMode, FileAccess, FileStat, io_error, FilePermission};
+            FileMode, FileAccess, FileStat, IoResult, FilePermission};
 use rt::rtio::{RtioFileStream, IoFactory, LocalIo};
 use io;
 use option::{Some, None, Option};
@@ -64,11 +68,12 @@ use vec::{OwnedVector, ImmutableVector};
 /// Can be constructed via `File::open()`, `File::create()`, and
 /// `File::open_mode()`.
 ///
-/// # Errors
+/// # Error
 ///
-/// This type will raise an io_error condition if operations are attempted against
-/// it for which its underlying file descriptor was not configured at creation
-/// time, via the `FileAccess` parameter to `File::open_mode()`.
+/// This type will return errors as an `IoResult<T>` if operations are
+/// attempted against it for which its underlying file descriptor was not
+/// configured at creation time, via the `FileAccess` parameter to
+/// `File::open_mode()`.
 pub struct File {
     priv fd: ~RtioFileStream,
     priv path: Path,
@@ -81,22 +86,19 @@ impl File {
     ///
     /// # Example
     ///
-    ///     use std::io::{File, io_error, Open, ReadWrite};
+    /// ```rust,should_fail
+    /// use std::io::{File, Open, ReadWrite};
     ///
-    ///     let p = Path::new("/some/file/path.txt");
+    /// let p = Path::new("/some/file/path.txt");
     ///
-    ///     io_error::cond.trap(|_| {
-    ///         // hoo-boy...
-    ///     }).inside(|| {
-    ///         let file = match File::open_mode(&p, Open, ReadWrite) {
-    ///             Some(s) => s,
-    ///             None => fail!("whoops! I'm sure this raised, anyways..")
-    ///         };
-    ///         // do some stuff with that file
+    /// let file = match File::open_mode(&p, Open, ReadWrite) {
+    ///     Ok(f) => f,
+    ///     Err(e) => fail!("file error: {}", e),
+    /// };
+    /// // do some stuff with that file
     ///
-    ///         // the file will be closed at the end of this block
-    ///     })
-    ///     // ..
+    /// // the file will be closed at the end of this block
+    /// ```
     ///
     /// `FileMode` and `FileAccess` provide information about the permissions
     /// context in which a given stream is created. More information about them
@@ -106,12 +108,12 @@ impl File {
     ///
     /// Note that, with this function, a `File` is returned regardless of the
     /// access-limitations indicated by `FileAccess` (e.g. calling `write` on a
-    /// `File` opened as `Read` will raise an `io_error` condition at runtime).
+    /// `File` opened as `Read` will return an error at runtime).
     ///
-    /// # Errors
+    /// # Error
     ///
-    /// This function will raise an `io_error` condition under a number of
-    /// different circumstances, to include but not limited to:
+    /// This function will return an error under a number of different
+    /// circumstances, to include but not limited to:
     ///
     /// * Opening a file that does not exist with `Read` access.
     /// * Attempting to open a file with a `FileAccess` that the user lacks
@@ -119,7 +121,7 @@ impl File {
     /// * Filesystem-level errors (full disk, etc)
     pub fn open_mode(path: &Path,
                      mode: FileMode,
-                     access: FileAccess) -> Option<File> {
+                     access: FileAccess) -> IoResult<File> {
         LocalIo::maybe_raise(|io| {
             io.fs_open(&path.to_c_str(), mode, access).map(|fd| {
                 File {
@@ -139,10 +141,12 @@ impl File {
     ///
     /// # Example
     ///
-    ///     use std::io::File;
+    /// ```rust
+    /// use std::io::File;
     ///
-    ///     let contents = File::open(&Path::new("foo.txt")).read_to_end();
-    pub fn open(path: &Path) -> Option<File> {
+    /// let contents = File::open(&Path::new("foo.txt")).read_to_end();
+    /// ```
+    pub fn open(path: &Path) -> IoResult<File> {
         File::open_mode(path, Open, Read)
     }
 
@@ -154,11 +158,16 @@ impl File {
     ///
     /// # Example
     ///
-    ///     use std::io::File;
+    /// ```rust
+    /// # #[allow(unused_must_use)];
+    /// use std::io::File;
     ///
-    ///     let mut f = File::create(&Path::new("foo.txt"));
-    ///     f.write(bytes!("This is a sample file"));
-    pub fn create(path: &Path) -> Option<File> {
+    /// let mut f = File::create(&Path::new("foo.txt"));
+    /// f.write(bytes!("This is a sample file"));
+    /// # drop(f);
+    /// # ::std::io::fs::unlink(&Path::new("foo.txt"));
+    /// ```
+    pub fn create(path: &Path) -> IoResult<File> {
         File::open_mode(path, Truncate, Write)
     }
 
@@ -170,24 +179,16 @@ impl File {
     /// Synchronizes all modifications to this file to its permanent storage
     /// device. This will flush any internal buffers necessary to perform this
     /// operation.
-    ///
-    /// # Errors
-    ///
-    /// This function will raise on the `io_error` condition on failure.
-    pub fn fsync(&mut self) {
-        let _ = self.fd.fsync().map_err(|e| io_error::cond.raise(e));
+    pub fn fsync(&mut self) -> IoResult<()> {
+        self.fd.fsync()
     }
 
     /// This function is similar to `fsync`, except that it may not synchronize
     /// file metadata to the filesystem. This is intended for use case which
     /// must synchronize content, but don't need the metadata on disk. The goal
     /// of this method is to reduce disk operations.
-    ///
-    /// # Errors
-    ///
-    /// This function will raise on the `io_error` condition on failure.
-    pub fn datasync(&mut self) {
-        let _ = self.fd.datasync().map_err(|e| io_error::cond.raise(e));
+    pub fn datasync(&mut self) -> IoResult<()> {
+        self.fd.datasync()
     }
 
     /// Either truncates or extends the underlying file, updating the size of
@@ -198,12 +199,8 @@ impl File {
     /// be shrunk. If it is greater than the current file's size, then the file
     /// will be extended to `size` and have all of the intermediate data filled
     /// in with 0s.
-    ///
-    /// # Errors
-    ///
-    /// On error, this function will raise on the `io_error` condition.
-    pub fn truncate(&mut self, size: i64) {
-        let _ = self.fd.truncate(size).map_err(|e| io_error::cond.raise(e));
+    pub fn truncate(&mut self, size: i64) -> IoResult<()> {
+        self.fd.truncate(size)
     }
 
     /// Tests whether this stream has reached EOF.
@@ -219,24 +216,25 @@ impl File {
 ///
 /// # Example
 ///
-///     use std::io::fs;
+/// ```rust
+/// # #[allow(unused_must_use)];
+/// use std::io::fs;
 ///
-///     let p = Path::new("/some/file/path.txt");
-///     fs::unlink(&p);
-///     // if we made it here without failing, then the
-///     // unlink operation was successful
+/// let p = Path::new("/some/file/path.txt");
+/// fs::unlink(&p);
+/// ```
 ///
 /// Note that, just because an unlink call was successful, it is not
 /// guaranteed that a file is immediately deleted (e.g. depending on
 /// platform, other open file descriptors may prevent immediate removal)
 ///
-/// # Errors
+/// # Error
 ///
-/// This function will raise an `io_error` condition if the path points to a
-/// directory, the user lacks permissions to remove the file, or if some
-/// other filesystem-level error occurs.
-pub fn unlink(path: &Path) {
-    LocalIo::maybe_raise(|io| io.fs_unlink(&path.to_c_str()));
+/// This function will return an error if the path points to a directory, the
+/// user lacks permissions to remove the file, or if some other filesystem-level
+/// error occurs.
+pub fn unlink(path: &Path) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_unlink(&path.to_c_str()))
 }
 
 /// Given a path, query the file system to get information about a file,
@@ -249,48 +247,25 @@ pub fn unlink(path: &Path) {
 ///
 /// # Example
 ///
-///     use std::io;
-///     use std::io::fs;
+/// ```rust
+/// use std::io::fs;
 ///
-///     let p = Path::new("/some/file/path.txt");
-///     match io::result(|| fs::stat(&p)) {
-///         Ok(stat) => { /* ... */ }
-///         Err(e) => { /* handle error */ }
-///     }
+/// let p = Path::new("/some/file/path.txt");
+/// match fs::stat(&p) {
+///     Ok(stat) => { /* ... */ }
+///     Err(e) => { /* handle error */ }
+/// }
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// This call will raise an `io_error` condition if the user lacks the
-/// requisite permissions to perform a `stat` call on the given path or if
-/// there is no entry in the filesystem at the provided path.
-pub fn stat(path: &Path) -> FileStat {
+/// This call will return an error if the user lacks the requisite permissions
+/// to perform a `stat` call on the given path or if there is no entry in the
+/// filesystem at the provided path.
+pub fn stat(path: &Path) -> IoResult<FileStat> {
     LocalIo::maybe_raise(|io| {
         io.fs_stat(&path.to_c_str())
-    }).unwrap_or_else(dummystat)
-}
-
-fn dummystat() -> FileStat {
-    FileStat {
-        path: Path::new(""),
-        size: 0,
-        kind: io::TypeFile,
-        perm: 0,
-        created: 0,
-        modified: 0,
-        accessed: 0,
-        unstable: io::UnstableFileStat {
-            device: 0,
-            inode: 0,
-            rdev: 0,
-            nlink: 0,
-            uid: 0,
-            gid: 0,
-            blksize: 0,
-            blocks: 0,
-            flags: 0,
-            gen: 0,
-        }
-    }
+    })
 }
 
 /// Perform the same operation as the `stat` function, except that this
@@ -298,31 +273,33 @@ fn dummystat() -> FileStat {
 /// information about the symlink file instead of the file that it points
 /// to.
 ///
-/// # Errors
+/// # Error
 ///
 /// See `stat`
-pub fn lstat(path: &Path) -> FileStat {
+pub fn lstat(path: &Path) -> IoResult<FileStat> {
     LocalIo::maybe_raise(|io| {
         io.fs_lstat(&path.to_c_str())
-    }).unwrap_or_else(dummystat)
+    })
 }
 
 /// Rename a file or directory to a new name.
 ///
 /// # Example
 ///
-///     use std::io::fs;
+/// ```rust
+/// # #[allow(unused_must_use)];
+/// use std::io::fs;
 ///
-///     fs::rename(&Path::new("foo"), &Path::new("bar"));
-///     // Oh boy, nothing was raised!
+/// fs::rename(&Path::new("foo"), &Path::new("bar"));
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// Will raise an `io_error` condition if the provided `path` doesn't exist,
-/// the process lacks permissions to view the contents, or if some other
-/// intermittent I/O error occurs.
-pub fn rename(from: &Path, to: &Path) {
-    LocalIo::maybe_raise(|io| io.fs_rename(&from.to_c_str(), &to.to_c_str()));
+/// Will return an error if the provided `path` doesn't exist, the process lacks
+/// permissions to view the contents, or if some other intermittent I/O error
+/// occurs.
+pub fn rename(from: &Path, to: &Path) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_rename(&from.to_c_str(), &to.to_c_str()))
 }
 
 /// Copies the contents of one file to another. This function will also
@@ -333,15 +310,17 @@ pub fn rename(from: &Path, to: &Path) {
 ///
 /// # Example
 ///
-///     use std::io::fs;
+/// ```rust
+/// # #[allow(unused_must_use)];
+/// use std::io::fs;
 ///
-///     fs::copy(&Path::new("foo.txt"), &Path::new("bar.txt"));
-///     // Oh boy, nothing was raised!
+/// fs::copy(&Path::new("foo.txt"), &Path::new("bar.txt"));
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// Will raise an `io_error` condition is the following situations, but is
-/// not limited to just these cases:
+/// Will return an error in the following situations, but is not limited to
+/// just these cases:
 ///
 /// * The `from` path is not a file
 /// * The `from` file does not exist
@@ -351,27 +330,29 @@ pub fn rename(from: &Path, to: &Path) {
 /// Note that this copy is not atomic in that once the destination is
 /// ensured to not exist, there is nothing preventing the destination from
 /// being created and then destroyed by this operation.
-pub fn copy(from: &Path, to: &Path) {
+pub fn copy(from: &Path, to: &Path) -> IoResult<()> {
     if !from.is_file() {
-        return io_error::cond.raise(IoError {
+        return Err(IoError {
             kind: io::MismatchedFileTypeForOperation,
             desc: "the source path is not an existing file",
             detail: None,
-        });
+        })
     }
 
-    let mut reader = match File::open(from) { Some(f) => f, None => return };
-    let mut writer = match File::create(to) { Some(f) => f, None => return };
+    let mut reader = if_ok!(File::open(from));
+    let mut writer = if_ok!(File::create(to));
     let mut buf = [0, ..io::DEFAULT_BUF_SIZE];
 
     loop {
-        match reader.read(buf) {
-            Some(amt) => writer.write(buf.slice_to(amt)),
-            None => break
-        }
+        let amt = match reader.read(buf) {
+            Ok(n) => n,
+            Err(ref e) if e.kind == io::EndOfFile => { break }
+            Err(e) => return Err(e)
+        };
+        if_ok!(writer.write(buf.slice_to(amt)));
     }
 
-    chmod(to, from.stat().perm)
+    chmod(to, if_ok!(from.stat()).perm)
 }
 
 /// Changes the permission mode bits found on a file or a directory. This
@@ -379,61 +360,51 @@ pub fn copy(from: &Path, to: &Path) {
 ///
 /// # Example
 ///
-///     use std::io;
-///     use std::io::fs;
+/// ```rust
+/// # #[allow(unused_must_use)];
+/// use std::io;
+/// use std::io::fs;
 ///
-///     fs::chmod(&Path::new("file.txt"), io::UserFile);
-///     fs::chmod(&Path::new("file.txt"), io::UserRead | io::UserWrite);
-///     fs::chmod(&Path::new("dir"),      io::UserDir);
-///     fs::chmod(&Path::new("file.exe"), io::UserExec);
+/// fs::chmod(&Path::new("file.txt"), io::UserFile);
+/// fs::chmod(&Path::new("file.txt"), io::UserRead | io::UserWrite);
+/// fs::chmod(&Path::new("dir"),      io::UserDir);
+/// fs::chmod(&Path::new("file.exe"), io::UserExec);
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// If this function encounters an I/O error, it will raise on the `io_error`
-/// condition. Some possible error situations are not having the permission to
+/// If this function encounters an I/O error, it will return an `Err` value.
+/// Some possible error situations are not having the permission to
 /// change the attributes of a file or the file not existing.
-pub fn chmod(path: &Path, mode: io::FilePermission) {
-    LocalIo::maybe_raise(|io| io.fs_chmod(&path.to_c_str(), mode));
+pub fn chmod(path: &Path, mode: io::FilePermission) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_chmod(&path.to_c_str(), mode))
 }
 
 /// Change the user and group owners of a file at the specified path.
-///
-/// # Errors
-///
-/// This function will raise on the `io_error` condition on failure.
-pub fn chown(path: &Path, uid: int, gid: int) {
-    LocalIo::maybe_raise(|io| io.fs_chown(&path.to_c_str(), uid, gid));
+pub fn chown(path: &Path, uid: int, gid: int) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_chown(&path.to_c_str(), uid, gid))
 }
 
 /// Creates a new hard link on the filesystem. The `dst` path will be a
 /// link pointing to the `src` path. Note that systems often require these
 /// two paths to both be located on the same filesystem.
-///
-/// # Errors
-///
-/// This function will raise on the `io_error` condition on failure.
-pub fn link(src: &Path, dst: &Path) {
-    LocalIo::maybe_raise(|io| io.fs_link(&src.to_c_str(), &dst.to_c_str()));
+pub fn link(src: &Path, dst: &Path) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_link(&src.to_c_str(), &dst.to_c_str()))
 }
 
 /// Creates a new symbolic link on the filesystem. The `dst` path will be a
 /// symlink pointing to the `src` path.
-///
-/// # Errors
-///
-/// This function will raise on the `io_error` condition on failure.
-pub fn symlink(src: &Path, dst: &Path) {
-    LocalIo::maybe_raise(|io| io.fs_symlink(&src.to_c_str(), &dst.to_c_str()));
+pub fn symlink(src: &Path, dst: &Path) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_symlink(&src.to_c_str(), &dst.to_c_str()))
 }
 
 /// Reads a symlink, returning the file that the symlink points to.
 ///
-/// # Errors
+/// # Error
 ///
-/// This function will raise on the `io_error` condition on failure. Failure
-/// conditions include reading a file that does not exist or reading a file
-/// which is not a symlink.
-pub fn readlink(path: &Path) -> Option<Path> {
+/// This function will return an error on failure. Failure conditions include
+/// reading a file that does not exist or reading a file which is not a symlink.
+pub fn readlink(path: &Path) -> IoResult<Path> {
     LocalIo::maybe_raise(|io| io.fs_readlink(&path.to_c_str()))
 }
 
@@ -441,75 +412,85 @@ pub fn readlink(path: &Path) -> Option<Path> {
 ///
 /// # Example
 ///
-///     use std::libc::S_IRWXU;
-///     use std::io::fs;
+/// ```rust
+/// # #[allow(unused_must_use)];
+/// use std::io;
+/// use std::io::fs;
 ///
-///     let p = Path::new("/some/dir");
-///     fs::mkdir(&p, S_IRWXU as int);
-///     // If we got here, our directory exists! Hooray!
+/// let p = Path::new("/some/dir");
+/// fs::mkdir(&p, io::UserRWX);
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// This call will raise an `io_error` condition if the user lacks permissions
-/// to make a new directory at the provided path, or if the directory already
-/// exists.
-pub fn mkdir(path: &Path, mode: FilePermission) {
-    LocalIo::maybe_raise(|io| io.fs_mkdir(&path.to_c_str(), mode));
+/// This call will return an error if the user lacks permissions to make a new
+/// directory at the provided path, or if the directory already exists.
+pub fn mkdir(path: &Path, mode: FilePermission) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_mkdir(&path.to_c_str(), mode))
 }
 
 /// Remove an existing, empty directory
 ///
 /// # Example
 ///
-///     use std::io::fs;
+/// ```rust
+/// # #[allow(unused_must_use)];
+/// use std::io::fs;
 ///
-///     let p = Path::new("/some/dir");
-///     fs::rmdir(&p);
-///     // good riddance, you mean ol' directory
+/// let p = Path::new("/some/dir");
+/// fs::rmdir(&p);
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// This call will raise an `io_error` condition if the user lacks permissions
-/// to remove the directory at the provided path, or if the directory isn't
-/// empty.
-pub fn rmdir(path: &Path) {
-    LocalIo::maybe_raise(|io| io.fs_rmdir(&path.to_c_str()));
+/// This call will return an error if the user lacks permissions to remove the
+/// directory at the provided path, or if the directory isn't empty.
+pub fn rmdir(path: &Path) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_rmdir(&path.to_c_str()))
 }
 
 /// Retrieve a vector containing all entries within a provided directory
 ///
 /// # Example
 ///
-///     use std::io::fs;
-///
-///     // one possible implementation of fs::walk_dir only visiting files
-///     fn visit_dirs(dir: &Path, cb: |&Path|) {
-///         if dir.is_dir() {
-///             let contents = fs::readdir(dir).unwrap();
-///             for entry in contents.iter() {
-///                 if entry.is_dir() { visit_dirs(entry, cb); }
-///                 else { cb(entry); }
+/// ```rust
+/// use std::io;
+/// use std::io::fs;
+///
+/// // one possible implementation of fs::walk_dir only visiting files
+/// fn visit_dirs(dir: &Path, cb: |&Path|) -> io::IoResult<()> {
+///     if dir.is_dir() {
+///         let contents = if_ok!(fs::readdir(dir));
+///         for entry in contents.iter() {
+///             if entry.is_dir() {
+///                 if_ok!(visit_dirs(entry, |p| cb(p)));
+///             } else {
+///                 cb(entry);
 ///             }
 ///         }
-///         else { fail!("nope"); }
+///         Ok(())
+///     } else {
+///         Err(io::standard_error(io::InvalidInput))
 ///     }
+/// }
+/// ```
 ///
-/// # Errors
+/// # Error
 ///
-/// Will raise an `io_error` condition if the provided `from` doesn't exist,
-/// the process lacks permissions to view the contents or if the `path` points
-/// at a non-directory file
-pub fn readdir(path: &Path) -> ~[Path] {
+/// Will return an error if the provided `from` doesn't exist, the process lacks
+/// permissions to view the contents or if the `path` points at a non-directory
+/// file
+pub fn readdir(path: &Path) -> IoResult<~[Path]> {
     LocalIo::maybe_raise(|io| {
         io.fs_readdir(&path.to_c_str(), 0)
-    }).unwrap_or_else(|| ~[])
+    })
 }
 
 /// Returns an iterator which will recursively walk the directory structure
 /// rooted at `path`. The path given will not be iterated over, and this will
 /// perform iteration in a top-down order.
-pub fn walk_dir(path: &Path) -> Directories {
-    Directories { stack: readdir(path) }
+pub fn walk_dir(path: &Path) -> IoResult<Directories> {
+    Ok(Directories { stack: if_ok!(readdir(path)) })
 }
 
 /// An iterator which walks over a directory
@@ -522,7 +503,10 @@ impl Iterator<Path> for Directories {
         match self.stack.shift() {
             Some(path) => {
                 if path.is_dir() {
-                    self.stack.push_all_move(readdir(&path));
+                    match readdir(&path) {
+                        Ok(dirs) => { self.stack.push_all_move(dirs); }
+                        Err(..) => {}
+                    }
                 }
                 Some(path)
             }
@@ -534,19 +518,18 @@ impl Iterator<Path> for Directories {
 /// Recursively create a directory and all of its parent components if they
 /// are missing.
 ///
-/// # Errors
+/// # Error
 ///
-/// This function will raise on the `io_error` condition if an error
-/// happens, see `fs::mkdir` for more information about error conditions
-/// and performance.
-pub fn mkdir_recursive(path: &Path, mode: FilePermission) {
+/// This function will return an `Err` value if an error happens, see
+/// `fs::mkdir` for more information about error conditions and performance.
+pub fn mkdir_recursive(path: &Path, mode: FilePermission) -> IoResult<()> {
     // tjc: if directory exists but with different permissions,
     // should we return false?
     if path.is_dir() {
-        return
+        return Ok(())
     }
     if path.filename().is_some() {
-        mkdir_recursive(&path.dir_path(), mode);
+        if_ok!(mkdir_recursive(&path.dir_path(), mode));
     }
     mkdir(path, mode)
 }
@@ -554,92 +537,64 @@ pub fn mkdir_recursive(path: &Path, mode: FilePermission) {
 /// Removes a directory at this path, after removing all its contents. Use
 /// carefully!
 ///
-/// # Errors
+/// # Error
 ///
-/// This function will raise on the `io_error` condition if an error
-/// happens. See `file::unlink` and `fs::readdir` for possible error
-/// conditions.
-pub fn rmdir_recursive(path: &Path) {
-    let children = readdir(path);
+/// This function will return an `Err` value if an error happens. See
+/// `file::unlink` and `fs::readdir` for possible error conditions.
+pub fn rmdir_recursive(path: &Path) -> IoResult<()> {
+    let children = if_ok!(readdir(path));
     for child in children.iter() {
         if child.is_dir() {
-            rmdir_recursive(child);
+            if_ok!(rmdir_recursive(child));
         } else {
-            unlink(child);
+            if_ok!(unlink(child));
         }
     }
     // Directory should now be empty
-    rmdir(path);
+    rmdir(path)
 }
 
 /// Changes the timestamps for a file's last modification and access time.
 /// The file at the path specified will have its last access time set to
 /// `atime` and its modification time set to `mtime`. The times specified should
 /// be in milliseconds.
-///
-/// # Errors
-///
-/// This function will raise on the `io_error` condition if an error
-/// happens.
 // FIXME(#10301) these arguments should not be u64
-pub fn change_file_times(path: &Path, atime: u64, mtime: u64) {
-    LocalIo::maybe_raise(|io| io.fs_utime(&path.to_c_str(), atime, mtime));
+pub fn change_file_times(path: &Path, atime: u64, mtime: u64) -> IoResult<()> {
+    LocalIo::maybe_raise(|io| io.fs_utime(&path.to_c_str(), atime, mtime))
 }
 
 impl Reader for File {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         match self.fd.read(buf) {
             Ok(read) => {
                 self.last_nread = read;
                 match read {
-                    0 => None,
-                    _ => Some(read as uint)
+                    0 => Err(io::standard_error(io::EndOfFile)),
+                    _ => Ok(read as uint)
                 }
             },
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != io::EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                return None;
-            }
+            Err(e) => Err(e),
         }
     }
 }
 
 impl Writer for File {
-    fn write(&mut self, buf: &[u8]) {
-        match self.fd.write(buf) {
-            Ok(()) => (),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-            }
-        }
-    }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.fd.write(buf) }
 }
 
 impl Seek for File {
-    fn tell(&self) -> u64 {
-        let res = self.fd.tell();
-        match res {
-            Ok(cursor) => cursor,
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                return -1;
-            }
-        }
+    fn tell(&self) -> IoResult<u64> {
+        self.fd.tell()
     }
 
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
         match self.fd.seek(pos, style) {
             Ok(_) => {
                 // successful seek resets EOF indicator
                 self.last_nread = -1;
-                ()
-            },
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
+                Ok(())
             }
+            Err(e) => Err(e),
         }
     }
 }
@@ -650,17 +605,17 @@ impl path::Path {
     /// Consult the `file::stat` documentation for more info.
     ///
     /// This call preserves identical runtime/error semantics with `file::stat`.
-    pub fn stat(&self) -> FileStat { stat(self) }
+    pub fn stat(&self) -> IoResult<FileStat> { stat(self) }
 
     /// Boolean value indicator whether the underlying file exists on the local
     /// filesystem. This will return true if the path points to either a
     /// directory or a file.
     ///
-    /// # Errors
+    /// # Error
     ///
     /// Will not raise a condition
     pub fn exists(&self) -> bool {
-        io::result(|| self.stat()).is_ok()
+        self.stat().is_ok()
     }
 
     /// Whether the underlying implementation (be it a file path, or something
@@ -668,11 +623,11 @@ impl path::Path {
     /// to non-existent locations or directories or other non-regular files
     /// (named pipes, etc).
     ///
-    /// # Errors
+    /// # Error
     ///
     /// Will not raise a condition
     pub fn is_file(&self) -> bool {
-        match io::result(|| self.stat()) {
+        match self.stat() {
             Ok(s) => s.kind == io::TypeFile,
             Err(..) => false
         }
@@ -683,11 +638,11 @@ impl path::Path {
     /// Will return false for paths to non-existent locations or if the item is
     /// not a directory (eg files, named pipes, links, etc)
     ///
-    /// # Errors
+    /// # Error
     ///
     /// Will not raise a condition
     pub fn is_dir(&self) -> bool {
-        match io::result(|| self.stat()) {
+        match self.stat() {
             Ok(s) => s.kind == io::TypeDirectory,
             Err(..) => false
         }
@@ -698,8 +653,7 @@ impl path::Path {
 #[allow(unused_imports)]
 mod test {
     use prelude::*;
-    use io::{SeekSet, SeekCur, SeekEnd, io_error, Read, Open,
-             ReadWrite};
+    use io::{SeekSet, SeekCur, SeekEnd, Read, Open, ReadWrite};
     use io;
     use str;
     use io::fs::{File, rmdir, mkdir, readdir, rmdir_recursive,
@@ -729,7 +683,7 @@ mod test {
             // Gee, seeing how we're testing the fs module I sure hope that we
             // at least implement this correctly!
             let TempDir(ref p) = *self;
-            io::fs::rmdir_recursive(p);
+            io::fs::rmdir_recursive(p).unwrap();
         }
     }
 
@@ -737,7 +691,7 @@ mod test {
         use os;
         use rand;
         let ret = os::tmpdir().join(format!("rust-{}", rand::random::<u32>()));
-        io::fs::mkdir(&ret, io::UserRWX);
+        io::fs::mkdir(&ret, io::UserRWX).unwrap();
         TempDir(ret)
     }
 
@@ -747,7 +701,7 @@ mod test {
         let filename = &tmpdir.join("file_rt_io_file_test.txt");
         {
             let mut write_stream = File::open_mode(filename, Open, ReadWrite);
-            write_stream.write(message.as_bytes());
+            write_stream.write(message.as_bytes()).unwrap();
         }
         {
             let mut read_stream = File::open_mode(filename, Open, Read);
@@ -758,30 +712,20 @@ mod test {
             };
             assert_eq!(read_str, message.to_owned());
         }
-        unlink(filename);
+        unlink(filename).unwrap();
     })
 
     iotest!(fn invalid_path_raises() {
         let tmpdir = tmpdir();
         let filename = &tmpdir.join("file_that_does_not_exist.txt");
-        let mut called = false;
-        io_error::cond.trap(|_| {
-            called = true;
-        }).inside(|| {
-            let result = File::open_mode(filename, Open, Read);
-            assert!(result.is_none());
-        });
-        assert!(called);
+        let result = File::open_mode(filename, Open, Read);
+        assert!(result.is_err());
     })
 
     iotest!(fn file_test_iounlinking_invalid_path_should_raise_condition() {
         let tmpdir = tmpdir();
         let filename = &tmpdir.join("file_another_file_that_does_not_exist.txt");
-        let mut called = false;
-        io_error::cond.trap(|_| {
-            called = true;
-        }).inside(|| unlink(filename));
-        assert!(called);
+        assert!(unlink(filename).is_err());
     })
 
     iotest!(fn file_test_io_non_positional_read() {
@@ -791,20 +735,20 @@ mod test {
         let filename = &tmpdir.join("file_rt_io_file_test_positional.txt");
         {
             let mut rw_stream = File::open_mode(filename, Open, ReadWrite);
-            rw_stream.write(message.as_bytes());
+            rw_stream.write(message.as_bytes()).unwrap();
         }
         {
             let mut read_stream = File::open_mode(filename, Open, Read);
             {
                 let read_buf = read_mem.mut_slice(0, 4);
-                read_stream.read(read_buf);
+                read_stream.read(read_buf).unwrap();
             }
             {
                 let read_buf = read_mem.mut_slice(4, 8);
-                read_stream.read(read_buf);
+                read_stream.read(read_buf).unwrap();
             }
         }
-        unlink(filename);
+        unlink(filename).unwrap();
         let read_str = str::from_utf8(read_mem).unwrap();
         assert_eq!(read_str, message);
     })
@@ -819,16 +763,16 @@ mod test {
         let filename = &tmpdir.join("file_rt_io_file_test_seeking.txt");
         {
             let mut rw_stream = File::open_mode(filename, Open, ReadWrite);
-            rw_stream.write(message.as_bytes());
+            rw_stream.write(message.as_bytes()).unwrap();
         }
         {
             let mut read_stream = File::open_mode(filename, Open, Read);
-            read_stream.seek(set_cursor as i64, SeekSet);
-            tell_pos_pre_read = read_stream.tell();
-            read_stream.read(read_mem);
-            tell_pos_post_read = read_stream.tell();
+            read_stream.seek(set_cursor as i64, SeekSet).unwrap();
+            tell_pos_pre_read = read_stream.tell().unwrap();
+            read_stream.read(read_mem).unwrap();
+            tell_pos_post_read = read_stream.tell().unwrap();
         }
-        unlink(filename);
+        unlink(filename).unwrap();
         let read_str = str::from_utf8(read_mem).unwrap();
         assert_eq!(read_str, message.slice(4, 8));
         assert_eq!(tell_pos_pre_read, set_cursor);
@@ -845,15 +789,15 @@ mod test {
         let filename = &tmpdir.join("file_rt_io_file_test_seek_and_write.txt");
         {
             let mut rw_stream = File::open_mode(filename, Open, ReadWrite);
-            rw_stream.write(initial_msg.as_bytes());
-            rw_stream.seek(seek_idx as i64, SeekSet);
-            rw_stream.write(overwrite_msg.as_bytes());
+            rw_stream.write(initial_msg.as_bytes()).unwrap();
+            rw_stream.seek(seek_idx as i64, SeekSet).unwrap();
+            rw_stream.write(overwrite_msg.as_bytes()).unwrap();
         }
         {
             let mut read_stream = File::open_mode(filename, Open, Read);
-            read_stream.read(read_mem);
+            read_stream.read(read_mem).unwrap();
         }
-        unlink(filename);
+        unlink(filename).unwrap();
         let read_str = str::from_utf8(read_mem).unwrap();
         assert!(read_str == final_msg.to_owned());
     })
@@ -869,24 +813,24 @@ mod test {
         let filename = &tmpdir.join("file_rt_io_file_test_seek_shakedown.txt");
         {
             let mut rw_stream = File::open_mode(filename, Open, ReadWrite);
-            rw_stream.write(initial_msg.as_bytes());
+            rw_stream.write(initial_msg.as_bytes()).unwrap();
         }
         {
             let mut read_stream = File::open_mode(filename, Open, Read);
 
-            read_stream.seek(-4, SeekEnd);
-            read_stream.read(read_mem);
+            read_stream.seek(-4, SeekEnd).unwrap();
+            read_stream.read(read_mem).unwrap();
             assert_eq!(str::from_utf8(read_mem).unwrap(), chunk_three);
 
-            read_stream.seek(-9, SeekCur);
-            read_stream.read(read_mem);
+            read_stream.seek(-9, SeekCur).unwrap();
+            read_stream.read(read_mem).unwrap();
             assert_eq!(str::from_utf8(read_mem).unwrap(), chunk_two);
 
-            read_stream.seek(0, SeekSet);
-            read_stream.read(read_mem);
+            read_stream.seek(0, SeekSet).unwrap();
+            read_stream.read(read_mem).unwrap();
             assert_eq!(str::from_utf8(read_mem).unwrap(), chunk_one);
         }
-        unlink(filename);
+        unlink(filename).unwrap();
     })
 
     iotest!(fn file_test_stat_is_correct_on_is_file() {
@@ -895,36 +839,36 @@ mod test {
         {
             let mut fs = File::open_mode(filename, Open, ReadWrite);
             let msg = "hw";
-            fs.write(msg.as_bytes());
+            fs.write(msg.as_bytes()).unwrap();
         }
-        let stat_res = stat(filename);
+        let stat_res = stat(filename).unwrap();
         assert_eq!(stat_res.kind, io::TypeFile);
-        unlink(filename);
+        unlink(filename).unwrap();
     })
 
     iotest!(fn file_test_stat_is_correct_on_is_dir() {
         let tmpdir = tmpdir();
         let filename = &tmpdir.join("file_stat_correct_on_is_dir");
-        mkdir(filename, io::UserRWX);
-        let stat_res = filename.stat();
+        mkdir(filename, io::UserRWX).unwrap();
+        let stat_res = filename.stat().unwrap();
         assert!(stat_res.kind == io::TypeDirectory);
-        rmdir(filename);
+        rmdir(filename).unwrap();
     })
 
     iotest!(fn file_test_fileinfo_false_when_checking_is_file_on_a_directory() {
         let tmpdir = tmpdir();
         let dir = &tmpdir.join("fileinfo_false_on_dir");
-        mkdir(dir, io::UserRWX);
+        mkdir(dir, io::UserRWX).unwrap();
         assert!(dir.is_file() == false);
-        rmdir(dir);
+        rmdir(dir).unwrap();
     })
 
     iotest!(fn file_test_fileinfo_check_exists_before_and_after_file_creation() {
         let tmpdir = tmpdir();
         let file = &tmpdir.join("fileinfo_check_exists_b_and_a.txt");
-        File::create(file).write(bytes!("foo"));
+        File::create(file).write(bytes!("foo")).unwrap();
         assert!(file.exists());
-        unlink(file);
+        unlink(file).unwrap();
         assert!(!file.exists());
     })
 
@@ -932,10 +876,10 @@ mod test {
         let tmpdir = tmpdir();
         let dir = &tmpdir.join("before_and_after_dir");
         assert!(!dir.exists());
-        mkdir(dir, io::UserRWX);
+        mkdir(dir, io::UserRWX).unwrap();
         assert!(dir.exists());
         assert!(dir.is_dir());
-        rmdir(dir);
+        rmdir(dir).unwrap();
         assert!(!dir.exists());
     })
 
@@ -943,21 +887,21 @@ mod test {
         use std::str;
         let tmpdir = tmpdir();
         let dir = &tmpdir.join("di_readdir");
-        mkdir(dir, io::UserRWX);
+        mkdir(dir, io::UserRWX).unwrap();
         let prefix = "foo";
         for n in range(0,3) {
             let f = dir.join(format!("{}.txt", n));
-            let mut w = File::create(&f);
+            let mut w = File::create(&f).unwrap();
             let msg_str = (prefix + n.to_str().to_owned()).to_owned();
             let msg = msg_str.as_bytes();
-            w.write(msg);
+            w.write(msg).unwrap();
         }
-        let files = readdir(dir);
+        let files = readdir(dir).unwrap();
         let mut mem = [0u8, .. 4];
         for f in files.iter() {
             {
                 let n = f.filestem_str();
-                File::open(f).read(mem);
+                File::open(f).read(mem).unwrap();
                 let read_str = str::from_utf8(mem).unwrap();
                 let expected = match n {
                     None|Some("") => fail!("really shouldn't happen.."),
@@ -965,13 +909,13 @@ mod test {
                 };
                 assert_eq!(expected.as_slice(), read_str);
             }
-            unlink(f);
+            unlink(f).unwrap();
         }
-        rmdir(dir);
+        rmdir(dir).unwrap();
     })
 
     iotest!(fn recursive_mkdir_slash() {
-        mkdir_recursive(&Path::new("/"), io::UserRWX);
+        mkdir_recursive(&Path::new("/"), io::UserRWX).unwrap();
     })
 
     iotest!(fn unicode_path_is_dir() {
@@ -982,12 +926,12 @@ mod test {
 
         let mut dirpath = tmpdir.path().clone();
         dirpath.push(format!("test-가一ー你好"));
-        mkdir(&dirpath, io::UserRWX);
+        mkdir(&dirpath, io::UserRWX).unwrap();
         assert!(dirpath.is_dir());
 
         let mut filepath = dirpath;
         filepath.push("unicode-file-\uac00\u4e00\u30fc\u4f60\u597d.rs");
-        File::create(&filepath); // ignore return; touch only
+        File::create(&filepath).unwrap(); // ignore return; touch only
         assert!(!filepath.is_dir());
         assert!(filepath.exists());
     })
@@ -999,7 +943,7 @@ mod test {
         let tmpdir = tmpdir();
         let unicode = tmpdir.path();
         let unicode = unicode.join(format!("test-각丁ー再见"));
-        mkdir(&unicode, io::UserRWX);
+        mkdir(&unicode, io::UserRWX).unwrap();
         assert!(unicode.exists());
         assert!(!Path::new("test/unicode-bogus-path-각丁ー再见").exists());
     })
@@ -1007,7 +951,7 @@ mod test {
     iotest!(fn copy_file_does_not_exist() {
         let from = Path::new("test/nonexistent-bogus-path");
         let to = Path::new("test/other-bogus-path");
-        match io::result(|| copy(&from, &to)) {
+        match copy(&from, &to) {
             Ok(..) => fail!(),
             Err(..) => {
                 assert!(!from.exists());
@@ -1021,20 +965,20 @@ mod test {
         let input = tmpdir.join("in.txt");
         let out = tmpdir.join("out.txt");
 
-        File::create(&input).write(bytes!("hello"));
-        copy(&input, &out);
-        let contents = File::open(&out).read_to_end();
+        File::create(&input).write(bytes!("hello")).unwrap();
+        copy(&input, &out).unwrap();
+        let contents = File::open(&out).read_to_end().unwrap();
         assert_eq!(contents.as_slice(), bytes!("hello"));
 
-        assert_eq!(input.stat().perm, out.stat().perm);
+        assert_eq!(input.stat().unwrap().perm, out.stat().unwrap().perm);
     })
 
     iotest!(fn copy_file_dst_dir() {
         let tmpdir = tmpdir();
         let out = tmpdir.join("out");
 
-        File::create(&out);
-        match io::result(|| copy(&out, tmpdir.path())) {
+        File::create(&out).unwrap();
+        match copy(&out, tmpdir.path()) {
             Ok(..) => fail!(), Err(..) => {}
         }
     })
@@ -1044,11 +988,11 @@ mod test {
         let input = tmpdir.join("in");
         let output = tmpdir.join("out");
 
-        File::create(&input).write("foo".as_bytes());
-        File::create(&output).write("bar".as_bytes());
-        copy(&input, &output);
+        File::create(&input).write("foo".as_bytes()).unwrap();
+        File::create(&output).write("bar".as_bytes()).unwrap();
+        copy(&input, &output).unwrap();
 
-        assert_eq!(File::open(&output).read_to_end(),
+        assert_eq!(File::open(&output).read_to_end().unwrap(),
                    (bytes!("foo")).to_owned());
     })
 
@@ -1056,7 +1000,7 @@ mod test {
         let tmpdir = tmpdir();
         let out = tmpdir.join("out");
 
-        match io::result(|| copy(tmpdir.path(), &out)) {
+        match copy(tmpdir.path(), &out) {
             Ok(..) => fail!(), Err(..) => {}
         }
         assert!(!out.exists());
@@ -1067,13 +1011,13 @@ mod test {
         let input = tmpdir.join("in.txt");
         let out = tmpdir.join("out.txt");
 
-        File::create(&input);
-        chmod(&input, io::UserRead);
-        copy(&input, &out);
-        assert!(out.stat().perm & io::UserWrite == 0);
+        File::create(&input).unwrap();
+        chmod(&input, io::UserRead).unwrap();
+        copy(&input, &out).unwrap();
+        assert!(out.stat().unwrap().perm & io::UserWrite == 0);
 
-        chmod(&input, io::UserFile);
-        chmod(&out, io::UserFile);
+        chmod(&input, io::UserFile).unwrap();
+        chmod(&out, io::UserFile).unwrap();
     })
 
     #[cfg(not(windows))] // FIXME(#10264) operation not permitted?
@@ -1082,26 +1026,27 @@ mod test {
         let input = tmpdir.join("in.txt");
         let out = tmpdir.join("out.txt");
 
-        File::create(&input).write("foobar".as_bytes());
-        symlink(&input, &out);
+        File::create(&input).write("foobar".as_bytes()).unwrap();
+        symlink(&input, &out).unwrap();
         if cfg!(not(windows)) {
-            assert_eq!(lstat(&out).kind, io::TypeSymlink);
+            assert_eq!(lstat(&out).unwrap().kind, io::TypeSymlink);
         }
-        assert_eq!(stat(&out).size, stat(&input).size);
-        assert_eq!(File::open(&out).read_to_end(), (bytes!("foobar")).to_owned());
+        assert_eq!(stat(&out).unwrap().size, stat(&input).unwrap().size);
+        assert_eq!(File::open(&out).read_to_end().unwrap(),
+                   (bytes!("foobar")).to_owned());
     })
 
     #[cfg(not(windows))] // apparently windows doesn't like symlinks
     iotest!(fn symlink_noexist() {
         let tmpdir = tmpdir();
         // symlinks can point to things that don't exist
-        symlink(&tmpdir.join("foo"), &tmpdir.join("bar"));
+        symlink(&tmpdir.join("foo"), &tmpdir.join("bar")).unwrap();
         assert!(readlink(&tmpdir.join("bar")).unwrap() == tmpdir.join("foo"));
     })
 
     iotest!(fn readlink_not_symlink() {
         let tmpdir = tmpdir();
-        match io::result(|| readlink(tmpdir.path())) {
+        match readlink(tmpdir.path()) {
             Ok(..) => fail!("wanted a failure"),
             Err(..) => {}
         }
@@ -1112,22 +1057,23 @@ mod test {
         let input = tmpdir.join("in.txt");
         let out = tmpdir.join("out.txt");
 
-        File::create(&input).write("foobar".as_bytes());
-        link(&input, &out);
+        File::create(&input).write("foobar".as_bytes()).unwrap();
+        link(&input, &out).unwrap();
         if cfg!(not(windows)) {
-            assert_eq!(lstat(&out).kind, io::TypeFile);
-            assert_eq!(stat(&out).unstable.nlink, 2);
+            assert_eq!(lstat(&out).unwrap().kind, io::TypeFile);
+            assert_eq!(stat(&out).unwrap().unstable.nlink, 2);
         }
-        assert_eq!(stat(&out).size, stat(&input).size);
-        assert_eq!(File::open(&out).read_to_end(), (bytes!("foobar")).to_owned());
+        assert_eq!(stat(&out).unwrap().size, stat(&input).unwrap().size);
+        assert_eq!(File::open(&out).read_to_end().unwrap(),
+                   (bytes!("foobar")).to_owned());
 
         // can't link to yourself
-        match io::result(|| link(&input, &input)) {
+        match link(&input, &input) {
             Ok(..) => fail!("wanted a failure"),
             Err(..) => {}
         }
         // can't link to something that doesn't exist
-        match io::result(|| link(&tmpdir.join("foo"), &tmpdir.join("bar"))) {
+        match link(&tmpdir.join("foo"), &tmpdir.join("bar")) {
             Ok(..) => fail!("wanted a failure"),
             Err(..) => {}
         }
@@ -1137,17 +1083,17 @@ mod test {
         let tmpdir = tmpdir();
         let file = tmpdir.join("in.txt");
 
-        File::create(&file);
-        assert!(stat(&file).perm & io::UserWrite == io::UserWrite);
-        chmod(&file, io::UserRead);
-        assert!(stat(&file).perm & io::UserWrite == 0);
+        File::create(&file).unwrap();
+        assert!(stat(&file).unwrap().perm & io::UserWrite == io::UserWrite);
+        chmod(&file, io::UserRead).unwrap();
+        assert!(stat(&file).unwrap().perm & io::UserWrite == 0);
 
-        match io::result(|| chmod(&tmpdir.join("foo"), io::UserRWX)) {
+        match chmod(&tmpdir.join("foo"), io::UserRWX) {
             Ok(..) => fail!("wanted a failure"),
             Err(..) => {}
         }
 
-        chmod(&file, io::UserFile);
+        chmod(&file, io::UserFile).unwrap();
     })
 
     iotest!(fn sync_doesnt_kill_anything() {
@@ -1155,11 +1101,11 @@ mod test {
         let path = tmpdir.join("in.txt");
 
         let mut file = File::open_mode(&path, io::Open, io::ReadWrite).unwrap();
-        file.fsync();
-        file.datasync();
-        file.write(bytes!("foo"));
-        file.fsync();
-        file.datasync();
+        file.fsync().unwrap();
+        file.datasync().unwrap();
+        file.write(bytes!("foo")).unwrap();
+        file.fsync().unwrap();
+        file.datasync().unwrap();
         drop(file);
     })
 
@@ -1168,28 +1114,28 @@ mod test {
         let path = tmpdir.join("in.txt");
 
         let mut file = File::open_mode(&path, io::Open, io::ReadWrite).unwrap();
-        file.write(bytes!("foo"));
-        file.fsync();
+        file.write(bytes!("foo")).unwrap();
+        file.fsync().unwrap();
 
         // Do some simple things with truncation
-        assert_eq!(stat(&path).size, 3);
-        file.truncate(10);
-        assert_eq!(stat(&path).size, 10);
-        file.write(bytes!("bar"));
-        file.fsync();
-        assert_eq!(stat(&path).size, 10);
-        assert_eq!(File::open(&path).read_to_end(),
+        assert_eq!(stat(&path).unwrap().size, 3);
+        file.truncate(10).unwrap();
+        assert_eq!(stat(&path).unwrap().size, 10);
+        file.write(bytes!("bar")).unwrap();
+        file.fsync().unwrap();
+        assert_eq!(stat(&path).unwrap().size, 10);
+        assert_eq!(File::open(&path).read_to_end().unwrap(),
                    (bytes!("foobar", 0, 0, 0, 0)).to_owned());
 
         // Truncate to a smaller length, don't seek, and then write something.
         // Ensure that the intermediate zeroes are all filled in (we're seeked
         // past the end of the file).
-        file.truncate(2);
-        assert_eq!(stat(&path).size, 2);
-        file.write(bytes!("wut"));
-        file.fsync();
-        assert_eq!(stat(&path).size, 9);
-        assert_eq!(File::open(&path).read_to_end(),
+        file.truncate(2).unwrap();
+        assert_eq!(stat(&path).unwrap().size, 2);
+        file.write(bytes!("wut")).unwrap();
+        file.fsync().unwrap();
+        assert_eq!(stat(&path).unwrap().size, 9);
+        assert_eq!(File::open(&path).read_to_end().unwrap(),
                    (bytes!("fo", 0, 0, 0, 0, "wut")).to_owned());
         drop(file);
     })
@@ -1197,8 +1143,7 @@ mod test {
     iotest!(fn open_flavors() {
         let tmpdir = tmpdir();
 
-        match io::result(|| File::open_mode(&tmpdir.join("a"), io::Open,
-                                            io::Read)) {
+        match File::open_mode(&tmpdir.join("a"), io::Open, io::Read) {
             Ok(..) => fail!(), Err(..) => {}
         }
         File::open_mode(&tmpdir.join("b"), io::Open, io::Write).unwrap();
@@ -1208,46 +1153,46 @@ mod test {
         File::open_mode(&tmpdir.join("f"), io::Truncate, io::Write).unwrap();
         File::open_mode(&tmpdir.join("g"), io::Truncate, io::ReadWrite).unwrap();
 
-        File::create(&tmpdir.join("h")).write("foo".as_bytes());
+        File::create(&tmpdir.join("h")).write("foo".as_bytes()).unwrap();
         File::open_mode(&tmpdir.join("h"), io::Open, io::Read).unwrap();
         {
             let mut f = File::open_mode(&tmpdir.join("h"), io::Open,
                                         io::Read).unwrap();
-            match io::result(|| f.write("wut".as_bytes())) {
+            match f.write("wut".as_bytes()) {
                 Ok(..) => fail!(), Err(..) => {}
             }
         }
-        assert_eq!(stat(&tmpdir.join("h")).size, 3);
+        assert_eq!(stat(&tmpdir.join("h")).unwrap().size, 3);
         {
             let mut f = File::open_mode(&tmpdir.join("h"), io::Append,
                                         io::Write).unwrap();
-            f.write("bar".as_bytes());
+            f.write("bar".as_bytes()).unwrap();
         }
-        assert_eq!(stat(&tmpdir.join("h")).size, 6);
+        assert_eq!(stat(&tmpdir.join("h")).unwrap().size, 6);
         {
             let mut f = File::open_mode(&tmpdir.join("h"), io::Truncate,
                                         io::Write).unwrap();
-            f.write("bar".as_bytes());
+            f.write("bar".as_bytes()).unwrap();
         }
-        assert_eq!(stat(&tmpdir.join("h")).size, 3);
+        assert_eq!(stat(&tmpdir.join("h")).unwrap().size, 3);
     })
 
     #[test]
     fn utime() {
         let tmpdir = tmpdir();
         let path = tmpdir.join("a");
-        File::create(&path);
+        File::create(&path).unwrap();
 
-        change_file_times(&path, 1000, 2000);
-        assert_eq!(path.stat().accessed, 1000);
-        assert_eq!(path.stat().modified, 2000);
+        change_file_times(&path, 1000, 2000).unwrap();
+        assert_eq!(path.stat().unwrap().accessed, 1000);
+        assert_eq!(path.stat().unwrap().modified, 2000);
     }
 
     #[test]
     fn utime_noexist() {
         let tmpdir = tmpdir();
 
-        match io::result(|| change_file_times(&tmpdir.join("a"), 100, 200)) {
+        match change_file_times(&tmpdir.join("a"), 100, 200) {
             Ok(..) => fail!(),
             Err(..) => {}
         }
diff --git a/src/libstd/io/mem.rs b/src/libstd/io/mem.rs
index c185951feca..395ece17ede 100644
--- a/src/libstd/io/mem.rs
+++ b/src/libstd/io/mem.rs
@@ -13,9 +13,10 @@
 use cmp::max;
 use cmp::min;
 use container::Container;
-use option::{Option, Some, None};
-use super::{Reader, Writer, Seek, Buffer, IoError, SeekStyle, io_error,
-            OtherIoError};
+use option::None;
+use result::{Err, Ok};
+use io;
+use io::{Reader, Writer, Seek, Buffer, IoError, SeekStyle, IoResult};
 use vec;
 use vec::{Vector, ImmutableVector, MutableVector, OwnedCloneableVector};
 
@@ -24,6 +25,7 @@ use vec::{Vector, ImmutableVector, MutableVector, OwnedCloneableVector};
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::MemWriter;
 ///
 /// let mut w = MemWriter::new();
@@ -59,7 +61,7 @@ impl MemWriter {
 }
 
 impl Writer for MemWriter {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         // Make sure the internal buffer is as least as big as where we
         // currently are
         let difference = self.pos as i64 - self.buf.len() as i64;
@@ -86,14 +88,15 @@ impl Writer for MemWriter {
 
         // Bump us forward
         self.pos += buf.len();
+        Ok(())
     }
 }
 
 // FIXME(#10432)
 impl Seek for MemWriter {
-    fn tell(&self) -> u64 { self.pos as u64 }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
 
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
         // compute offset as signed and clamp to prevent overflow
         let offset = match style {
             SeekSet => { 0 }
@@ -102,6 +105,7 @@ impl Seek for MemWriter {
         } as i64;
 
         self.pos = max(0, offset+pos) as uint;
+        Ok(())
     }
 }
 
@@ -110,11 +114,12 @@ impl Seek for MemWriter {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::MemReader;
 ///
 /// let mut r = MemReader::new(~[0, 1, 2]);
 ///
-/// assert_eq!(r.read_to_end(), ~[0, 1, 2]);
+/// assert_eq!(r.read_to_end().unwrap(), ~[0, 1, 2]);
 /// ```
 pub struct MemReader {
     priv buf: ~[u8],
@@ -148,8 +153,8 @@ impl MemReader {
 }
 
 impl Reader for MemReader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        if self.eof() { return None }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        if self.eof() { return Err(io::standard_error(io::EndOfFile)) }
 
         let write_len = min(buf.len(), self.buf.len() - self.pos);
         {
@@ -161,28 +166,31 @@ impl Reader for MemReader {
         self.pos += write_len;
         assert!(self.pos <= self.buf.len());
 
-        return Some(write_len);
+        return Ok(write_len);
     }
 }
 
 impl Seek for MemReader {
-    fn tell(&self) -> u64 { self.pos as u64 }
-    fn seek(&mut self, _pos: i64, _style: SeekStyle) { fail!() }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
+    fn seek(&mut self, _pos: i64, _style: SeekStyle) -> IoResult<()> { fail!() }
 }
 
 impl Buffer for MemReader {
-    fn fill<'a>(&'a mut self) -> &'a [u8] { self.buf.slice_from(self.pos) }
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> {
+        Ok(self.buf.slice_from(self.pos))
+    }
     fn consume(&mut self, amt: uint) { self.pos += amt; }
 }
 
 /// Writes to a fixed-size byte slice
 ///
-/// If a write will not fit in the buffer, it raises the `io_error`
-/// condition and does not write any data.
+/// If a write will not fit in the buffer, it returns an error and does not
+/// write any data.
 ///
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::BufWriter;
 ///
 /// let mut buf = [0, ..4];
@@ -207,28 +215,28 @@ impl<'a> BufWriter<'a> {
 }
 
 impl<'a> Writer for BufWriter<'a> {
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
         // raises a condition if the entire write does not fit in the buffer
         let max_size = self.buf.len();
         if self.pos >= max_size || (self.pos + buf.len()) > max_size {
-            io_error::cond.raise(IoError {
-                kind: OtherIoError,
+            return Err(IoError {
+                kind: io::OtherIoError,
                 desc: "Trying to write past end of buffer",
                 detail: None
-            });
-            return;
+            })
         }
 
         vec::bytes::copy_memory(self.buf.mut_slice_from(self.pos), buf);
         self.pos += buf.len();
+        Ok(())
     }
 }
 
 // FIXME(#10432)
 impl<'a> Seek for BufWriter<'a> {
-    fn tell(&self) -> u64 { self.pos as u64 }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
 
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
         // compute offset as signed and clamp to prevent overflow
         let offset = match style {
             SeekSet => { 0 }
@@ -237,6 +245,7 @@ impl<'a> Seek for BufWriter<'a> {
         } as i64;
 
         self.pos = max(0, offset+pos) as uint;
+        Ok(())
     }
 }
 
@@ -246,12 +255,13 @@ impl<'a> Seek for BufWriter<'a> {
 /// # Example
 ///
 /// ```rust
+/// # #[allow(unused_must_use)];
 /// use std::io::BufReader;
 ///
 /// let mut buf = [0, 1, 2, 3];
 /// let mut r = BufReader::new(buf);
 ///
-/// assert_eq!(r.read_to_end(), ~[0, 1, 2, 3]);
+/// assert_eq!(r.read_to_end().unwrap(), ~[0, 1, 2, 3]);
 /// ```
 pub struct BufReader<'a> {
     priv buf: &'a [u8],
@@ -274,8 +284,8 @@ impl<'a> BufReader<'a> {
 }
 
 impl<'a> Reader for BufReader<'a> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        if self.eof() { return None }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        if self.eof() { return Err(io::standard_error(io::EndOfFile)) }
 
         let write_len = min(buf.len(), self.buf.len() - self.pos);
         {
@@ -287,18 +297,19 @@ impl<'a> Reader for BufReader<'a> {
         self.pos += write_len;
         assert!(self.pos <= self.buf.len());
 
-        return Some(write_len);
+        return Ok(write_len);
      }
 }
 
 impl<'a> Seek for BufReader<'a> {
-    fn tell(&self) -> u64 { self.pos as u64 }
-
-    fn seek(&mut self, _pos: i64, _style: SeekStyle) { fail!() }
+    fn tell(&self) -> IoResult<u64> { Ok(self.pos as u64) }
+    fn seek(&mut self, _pos: i64, _style: SeekStyle) -> IoResult<()> { fail!() }
 }
 
 impl<'a> Buffer for BufReader<'a> {
-    fn fill<'a>(&'a mut self) -> &'a [u8] { self.buf.slice_from(self.pos) }
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]> {
+        Ok(self.buf.slice_from(self.pos))
+    }
     fn consume(&mut self, amt: uint) { self.pos += amt; }
 }
 
@@ -307,33 +318,34 @@ mod test {
     use prelude::*;
     use super::*;
     use io::*;
+    use io;
 
     #[test]
     fn test_mem_writer() {
         let mut writer = MemWriter::new();
-        assert_eq!(writer.tell(), 0);
-        writer.write([0]);
-        assert_eq!(writer.tell(), 1);
-        writer.write([1, 2, 3]);
-        writer.write([4, 5, 6, 7]);
-        assert_eq!(writer.tell(), 8);
+        assert_eq!(writer.tell(), Ok(0));
+        writer.write([0]).unwrap();
+        assert_eq!(writer.tell(), Ok(1));
+        writer.write([1, 2, 3]).unwrap();
+        writer.write([4, 5, 6, 7]).unwrap();
+        assert_eq!(writer.tell(), Ok(8));
         assert_eq!(writer.get_ref(), [0, 1, 2, 3, 4, 5, 6, 7]);
 
-        writer.seek(0, SeekSet);
-        assert_eq!(writer.tell(), 0);
-        writer.write([3, 4]);
+        writer.seek(0, SeekSet).unwrap();
+        assert_eq!(writer.tell(), Ok(0));
+        writer.write([3, 4]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 3, 4, 5, 6, 7]);
 
-        writer.seek(1, SeekCur);
-        writer.write([0, 1]);
+        writer.seek(1, SeekCur).unwrap();
+        writer.write([0, 1]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 0, 1, 5, 6, 7]);
 
-        writer.seek(-1, SeekEnd);
-        writer.write([1, 2]);
+        writer.seek(-1, SeekEnd).unwrap();
+        writer.write([1, 2]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 0, 1, 5, 6, 1, 2]);
 
-        writer.seek(1, SeekEnd);
-        writer.write([1]);
+        writer.seek(1, SeekEnd).unwrap();
+        writer.write([1]).unwrap();
         assert_eq!(writer.get_ref(), [3, 4, 2, 0, 1, 5, 6, 1, 2, 0, 1]);
     }
 
@@ -342,12 +354,12 @@ mod test {
         let mut buf = [0 as u8, ..8];
         {
             let mut writer = BufWriter::new(buf);
-            assert_eq!(writer.tell(), 0);
-            writer.write([0]);
-            assert_eq!(writer.tell(), 1);
-            writer.write([1, 2, 3]);
-            writer.write([4, 5, 6, 7]);
-            assert_eq!(writer.tell(), 8);
+            assert_eq!(writer.tell(), Ok(0));
+            writer.write([0]).unwrap();
+            assert_eq!(writer.tell(), Ok(1));
+            writer.write([1, 2, 3]).unwrap();
+            writer.write([4, 5, 6, 7]).unwrap();
+            assert_eq!(writer.tell(), Ok(8));
         }
         assert_eq!(buf, [0, 1, 2, 3, 4, 5, 6, 7]);
     }
@@ -357,24 +369,24 @@ mod test {
         let mut buf = [0 as u8, ..8];
         {
             let mut writer = BufWriter::new(buf);
-            assert_eq!(writer.tell(), 0);
-            writer.write([1]);
-            assert_eq!(writer.tell(), 1);
+            assert_eq!(writer.tell(), Ok(0));
+            writer.write([1]).unwrap();
+            assert_eq!(writer.tell(), Ok(1));
 
-            writer.seek(2, SeekSet);
-            assert_eq!(writer.tell(), 2);
-            writer.write([2]);
-            assert_eq!(writer.tell(), 3);
+            writer.seek(2, SeekSet).unwrap();
+            assert_eq!(writer.tell(), Ok(2));
+            writer.write([2]).unwrap();
+            assert_eq!(writer.tell(), Ok(3));
 
-            writer.seek(-2, SeekCur);
-            assert_eq!(writer.tell(), 1);
-            writer.write([3]);
-            assert_eq!(writer.tell(), 2);
+            writer.seek(-2, SeekCur).unwrap();
+            assert_eq!(writer.tell(), Ok(1));
+            writer.write([3]).unwrap();
+            assert_eq!(writer.tell(), Ok(2));
 
-            writer.seek(-1, SeekEnd);
-            assert_eq!(writer.tell(), 7);
-            writer.write([4]);
-            assert_eq!(writer.tell(), 8);
+            writer.seek(-1, SeekEnd).unwrap();
+            assert_eq!(writer.tell(), Ok(7));
+            writer.write([4]).unwrap();
+            assert_eq!(writer.tell(), Ok(8));
 
         }
         assert_eq!(buf, [1, 3, 2, 0, 0, 0, 0, 4]);
@@ -384,35 +396,31 @@ mod test {
     fn test_buf_writer_error() {
         let mut buf = [0 as u8, ..2];
         let mut writer = BufWriter::new(buf);
-        writer.write([0]);
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, OtherIoError);
-            called = true;
-        }).inside(|| {
-            writer.write([0, 0]);
-        });
-        assert!(called);
+        writer.write([0]).unwrap();
+
+        match writer.write([0, 0]) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::OtherIoError),
+        }
     }
 
     #[test]
     fn test_mem_reader() {
         let mut reader = MemReader::new(~[0, 1, 2, 3, 4, 5, 6, 7]);
         let mut buf = [];
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.tell(), 0);
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.tell(), Ok(0));
         let mut buf = [0];
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.tell(), 1);
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.tell(), Ok(1));
         assert_eq!(buf, [0]);
         let mut buf = [0, ..4];
-        assert_eq!(reader.read(buf), Some(4));
-        assert_eq!(reader.tell(), 5);
+        assert_eq!(reader.read(buf), Ok(4));
+        assert_eq!(reader.tell(), Ok(5));
         assert_eq!(buf, [1, 2, 3, 4]);
-        assert_eq!(reader.read(buf), Some(3));
+        assert_eq!(reader.read(buf), Ok(3));
         assert_eq!(buf.slice(0, 3), [5, 6, 7]);
-        assert_eq!(reader.read(buf), None);
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
@@ -420,64 +428,64 @@ mod test {
         let in_buf = ~[0, 1, 2, 3, 4, 5, 6, 7];
         let mut reader = BufReader::new(in_buf);
         let mut buf = [];
-        assert_eq!(reader.read(buf), Some(0));
-        assert_eq!(reader.tell(), 0);
+        assert_eq!(reader.read(buf), Ok(0));
+        assert_eq!(reader.tell(), Ok(0));
         let mut buf = [0];
-        assert_eq!(reader.read(buf), Some(1));
-        assert_eq!(reader.tell(), 1);
+        assert_eq!(reader.read(buf), Ok(1));
+        assert_eq!(reader.tell(), Ok(1));
         assert_eq!(buf, [0]);
         let mut buf = [0, ..4];
-        assert_eq!(reader.read(buf), Some(4));
-        assert_eq!(reader.tell(), 5);
+        assert_eq!(reader.read(buf), Ok(4));
+        assert_eq!(reader.tell(), Ok(5));
         assert_eq!(buf, [1, 2, 3, 4]);
-        assert_eq!(reader.read(buf), Some(3));
+        assert_eq!(reader.read(buf), Ok(3));
         assert_eq!(buf.slice(0, 3), [5, 6, 7]);
-        assert_eq!(reader.read(buf), None);
+        assert!(reader.read(buf).is_err());
     }
 
     #[test]
     fn test_read_char() {
         let b = bytes!("Việt");
         let mut r = BufReader::new(b);
-        assert_eq!(r.read_char(), Some('V'));
-        assert_eq!(r.read_char(), Some('i'));
-        assert_eq!(r.read_char(), Some('ệ'));
-        assert_eq!(r.read_char(), Some('t'));
-        assert_eq!(r.read_char(), None);
+        assert_eq!(r.read_char(), Ok('V'));
+        assert_eq!(r.read_char(), Ok('i'));
+        assert_eq!(r.read_char(), Ok('ệ'));
+        assert_eq!(r.read_char(), Ok('t'));
+        assert!(r.read_char().is_err());
     }
 
     #[test]
     fn test_read_bad_char() {
         let b = bytes!(0x80);
         let mut r = BufReader::new(b);
-        assert_eq!(r.read_char(), None);
+        assert!(r.read_char().is_err());
     }
 
     #[test]
     fn test_write_strings() {
         let mut writer = MemWriter::new();
-        writer.write_str("testing");
-        writer.write_line("testing");
-        writer.write_str("testing");
+        writer.write_str("testing").unwrap();
+        writer.write_line("testing").unwrap();
+        writer.write_str("testing").unwrap();
         let mut r = BufReader::new(writer.get_ref());
-        assert_eq!(r.read_to_str(), ~"testingtesting\ntesting");
+        assert_eq!(r.read_to_str().unwrap(), ~"testingtesting\ntesting");
     }
 
     #[test]
     fn test_write_char() {
         let mut writer = MemWriter::new();
-        writer.write_char('a');
-        writer.write_char('\n');
-        writer.write_char('ệ');
+        writer.write_char('a').unwrap();
+        writer.write_char('\n').unwrap();
+        writer.write_char('ệ').unwrap();
         let mut r = BufReader::new(writer.get_ref());
-        assert_eq!(r.read_to_str(), ~"a\nệ");
+        assert_eq!(r.read_to_str().unwrap(), ~"a\nệ");
     }
 
     #[test]
     fn test_read_whole_string_bad() {
         let buf = [0xff];
         let mut r = BufReader::new(buf);
-        match result(|| r.read_to_str()) {
+        match r.read_to_str() {
             Ok(..) => fail!(),
             Err(..) => {}
         }
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index 69f0cf96ffc..7690c88478f 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -29,7 +29,6 @@ Some examples of obvious things you might want to do
     use std::io::BufferedReader;
     use std::io::stdin;
 
-    # let _g = ::std::io::ignore_io_error();
     let mut stdin = BufferedReader::new(stdin());
     for line in stdin.lines() {
         print!("{}", line);
@@ -41,16 +40,15 @@ Some examples of obvious things you might want to do
     ```rust
     use std::io::File;
 
-    # let _g = ::std::io::ignore_io_error();
     let contents = File::open(&Path::new("message.txt")).read_to_end();
     ```
 
 * Write a line to a file
 
     ```rust
+    # #[allow(unused_must_use)];
     use std::io::File;
 
-    # let _g = ::std::io::ignore_io_error();
     let mut file = File::create(&Path::new("message.txt"));
     file.write(bytes!("hello, file!\n"));
     # drop(file);
@@ -63,7 +61,6 @@ Some examples of obvious things you might want to do
     use std::io::BufferedReader;
     use std::io::File;
 
-    # let _g = ::std::io::ignore_io_error();
     let path = Path::new("message.txt");
     let mut file = BufferedReader::new(File::open(&path));
     for line in file.lines() {
@@ -77,7 +74,6 @@ Some examples of obvious things you might want to do
     use std::io::BufferedReader;
     use std::io::File;
 
-    # let _g = ::std::io::ignore_io_error();
     let path = Path::new("message.txt");
     let mut file = BufferedReader::new(File::open(&path));
     let lines: ~[~str] = file.lines().collect();
@@ -88,10 +84,10 @@ Some examples of obvious things you might want to do
   `write_str` and `write_line` methods.
 
     ```rust,should_fail
+    # #[allow(unused_must_use)];
     use std::io::net::ip::SocketAddr;
     use std::io::net::tcp::TcpStream;
 
-    # let _g = ::std::io::ignore_io_error();
     let addr = from_str::<SocketAddr>("127.0.0.1:8080").unwrap();
     let mut socket = TcpStream::connect(addr).unwrap();
     socket.write(bytes!("GET / HTTP/1.0\n\n"));
@@ -168,72 +164,51 @@ asynchronous request completes.
 # Error Handling
 
 I/O is an area where nearly every operation can result in unexpected
-errors. It should allow errors to be handled efficiently.
-It needs to be convenient to use I/O when you don't care
-about dealing with specific errors.
+errors. Errors should be painfully visible when they happen, and handling them
+should be easy to work with. It should be convenient to handle specific I/O
+errors, and it should also be convenient to not deal with I/O errors.
 
 Rust's I/O employs a combination of techniques to reduce boilerplate
 while still providing feedback about errors. The basic strategy:
 
-* Errors are fatal by default, resulting in task failure
-* Errors raise the `io_error` condition which provides an opportunity to inspect
-  an IoError object containing details.
-* Return values must have a sensible null or zero value which is returned
-  if a condition is handled successfully. This may be an `Option`, an empty
-  vector, or other designated error value.
-* Common traits are implemented for `Option`, e.g. `impl<R: Reader> Reader for Option<R>`,
-  so that nullable values do not have to be 'unwrapped' before use.
+* All I/O operations return `IoResult<T>` which is equivalent to
+  `Result<T, IoError>`. The core `Result` type is defined in the `std::result`
+  module.
+* If the `Result` type goes unused, then the compiler will by default emit a
+  warning about the unused result.
+* Common traits are implemented for `IoResult`, e.g.
+  `impl<R: Reader> Reader for IoResult<R>`, so that error values do not have
+  to be 'unwrapped' before use.
 
 These features combine in the API to allow for expressions like
 `File::create(&Path::new("diary.txt")).write(bytes!("Met a girl.\n"))`
 without having to worry about whether "diary.txt" exists or whether
 the write succeeds. As written, if either `new` or `write_line`
-encounters an error the task will fail.
+encounters an error then the result of the entire expression will
+be an error.
 
 If you wanted to handle the error though you might write:
 
 ```rust
+# #[allow(unused_must_use)];
 use std::io::File;
-use std::io::{IoError, io_error};
 
-let mut error = None;
-io_error::cond.trap(|e: IoError| {
-    error = Some(e);
-}).inside(|| {
-    File::create(&Path::new("diary.txt")).write(bytes!("Met a girl.\n"));
-});
-
-if error.is_some() {
-    println!("failed to write my diary");
+match File::create(&Path::new("diary.txt")).write(bytes!("Met a girl.\n")) {
+    Ok(()) => { /* succeeded */ }
+    Err(e) => println!("failed to write to my diary: {}", e),
 }
+
 # ::std::io::fs::unlink(&Path::new("diary.txt"));
 ```
 
-FIXME: Need better condition handling syntax
-
-In this case the condition handler will have the opportunity to
-inspect the IoError raised by either the call to `new` or the call to
-`write_line`, but then execution will continue.
-
-So what actually happens if `new` encounters an error? To understand
-that it's important to know that what `new` returns is not a `File`
-but an `Option<File>`.  If the file does not open, and the condition
-is handled, then `new` will simply return `None`. Because there is an
-implementation of `Writer` (the trait required ultimately required for
-types to implement `write_line`) there is no need to inspect or unwrap
-the `Option<File>` and we simply call `write_line` on it.  If `new`
-returned a `None` then the followup call to `write_line` will also
-raise an error.
-
-## Concerns about this strategy
-
-This structure will encourage a programming style that is prone
-to errors similar to null pointer dereferences.
-In particular code written to ignore errors and expect conditions to be unhandled
-will start passing around null or zero objects when wrapped in a condition handler.
-
-* FIXME: How should we use condition handlers that return values?
-* FIXME: Should EOF raise default conditions when EOF is not an error?
+So what actually happens if `create` encounters an error?
+It's important to know that what `new` returns is not a `File`
+but an `IoResult<File>`.  If the file does not open, then `new` will simply
+return `Err(..)`. Because there is an implementation of `Writer` (the trait
+required ultimately required for types to implement `write_line`) there is no
+need to inspect or unwrap the `IoResult<File>` and we simply call `write_line`
+on it. If `new` returned an `Err(..)` then the followup call to `write_line`
+will also return an error.
 
 # Issues with i/o scheduler affinity, work stealing, task pinning
 
@@ -287,18 +262,19 @@ Out of scope
 */
 
 #[allow(missing_doc)];
+#[deny(unused_must_use)];
 
 use cast;
 use char::Char;
-use condition::Guard;
 use container::Container;
+use fmt;
 use int;
 use iter::Iterator;
 use option::{Option, Some, None};
 use path::Path;
 use result::{Ok, Err, Result};
-use str;
 use str::{StrSlice, OwnedStr};
+use str;
 use to_str::ToStr;
 use uint;
 use unstable::finally::Finally;
@@ -347,8 +323,8 @@ mod mem;
 /// Non-blocking access to stdin, stdout, stderr
 pub mod stdio;
 
-/// Implementations for Option
-mod option;
+/// Implementations for Result
+mod result;
 
 /// Extension traits
 pub mod extensions;
@@ -373,17 +349,30 @@ mod comm_adapters;
 // https://groups.google.com/forum/#!topic/libuv/oQO1HJAIDdA
 static DEFAULT_BUF_SIZE: uint = 1024 * 64;
 
+pub type IoResult<T> = Result<T, IoError>;
+
 /// The type passed to I/O condition handlers to indicate error
 ///
 /// # FIXME
 ///
 /// Is something like this sufficient? It's kind of archaic
+#[deriving(Eq, Clone)]
 pub struct IoError {
     kind: IoErrorKind,
     desc: &'static str,
     detail: Option<~str>
 }
 
+impl fmt::Show for IoError {
+    fn fmt(err: &IoError, fmt: &mut fmt::Formatter) -> fmt::Result {
+        if_ok!(fmt.buf.write_str(err.desc));
+        match err.detail {
+            Some(ref s) => write!(fmt.buf, " ({})", *s),
+            None => Ok(())
+        }
+    }
+}
+
 // FIXME: #8242 implementing manually because deriving doesn't work for some reason
 impl ToStr for IoError {
     fn to_str(&self) -> ~str {
@@ -398,9 +387,8 @@ impl ToStr for IoError {
     }
 }
 
-#[deriving(Eq)]
+#[deriving(Eq, Clone)]
 pub enum IoErrorKind {
-    PreviousIoError,
     OtherIoError,
     EndOfFile,
     FileNotFound,
@@ -424,7 +412,6 @@ pub enum IoErrorKind {
 impl ToStr for IoErrorKind {
     fn to_str(&self) -> ~str {
         match *self {
-            PreviousIoError => ~"PreviousIoError",
             OtherIoError => ~"OtherIoError",
             EndOfFile => ~"EndOfFile",
             FileNotFound => ~"FileNotFound",
@@ -446,184 +433,130 @@ impl ToStr for IoErrorKind {
     }
 }
 
-// FIXME: Can't put doc comments on macros
-// Raised by `I/O` operations on error.
-condition! {
-    pub io_error: IoError -> ();
-}
-
-/// Helper for wrapper calls where you want to
-/// ignore any io_errors that might be raised
-pub fn ignore_io_error() -> Guard<'static,IoError,()> {
-    io_error::cond.trap(|_| {
-        // just swallow the error.. downstream users
-        // who can make a decision based on a None result
-        // won't care
-    }).guard()
-}
-
-/// Helper for catching an I/O error and wrapping it in a Result object. The
-/// return result will be the last I/O error that happened or the result of the
-/// closure if no error occurred.
-pub fn result<T>(cb: || -> T) -> Result<T, IoError> {
-    let mut err = None;
-    let ret = io_error::cond.trap(|e| {
-        if err.is_none() {
-            err = Some(e);
-        }
-    }).inside(cb);
-    match err {
-        Some(e) => Err(e),
-        None => Ok(ret),
-    }
-}
-
 pub trait Reader {
 
-    // Only two methods which need to get implemented for this trait
+    // Only method which need to get implemented for this trait
 
     /// Read bytes, up to the length of `buf` and place them in `buf`.
     /// Returns the number of bytes read. The number of bytes read my
-    /// be less than the number requested, even 0. Returns `None` on EOF.
-    ///
-    /// # Failure
+    /// be less than the number requested, even 0. Returns `Err` on EOF.
     ///
-    /// Raises the `io_error` condition on error. If the condition
-    /// is handled then no guarantee is made about the number of bytes
-    /// read and the contents of `buf`. If the condition is handled
-    /// returns `None` (FIXME see below).
+    /// # Error
     ///
-    /// # FIXME
-    ///
-    /// * Should raise_default error on eof?
-    /// * If the condition is handled it should still return the bytes read,
-    ///   in which case there's no need to return Option - but then you *have*
-    ///   to install a handler to detect eof.
-    ///
-    /// This doesn't take a `len` argument like the old `read`.
-    /// Will people often need to slice their vectors to call this
-    /// and will that be annoying?
-    /// Is it actually possible for 0 bytes to be read successfully?
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint>;
+    /// If an error occurs during this I/O operation, then it is returned as
+    /// `Err(IoError)`. Note that end-of-file is considered an error, and can be
+    /// inspected for in the error's `kind` field. Also note that reading 0
+    /// bytes is not considered an error in all circumstances
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint>;
 
     // Convenient helper methods based on the above methods
 
-    /// Reads a single byte. Returns `None` on EOF.
-    ///
-    /// # Failure
-    ///
-    /// Raises the same conditions as the `read` method. Returns
-    /// `None` if the condition is handled.
-    fn read_byte(&mut self) -> Option<u8> {
+    /// Reads a single byte. Returns `Err` on EOF.
+    fn read_byte(&mut self) -> IoResult<u8> {
         let mut buf = [0];
-        match self.read(buf) {
-            Some(0) => {
-                debug!("read 0 bytes. trying again");
-                self.read_byte()
+        loop {
+            match self.read(buf) {
+                Ok(0) => {
+                    debug!("read 0 bytes. trying again");
+                }
+                Ok(1) => return Ok(buf[0]),
+                Ok(_) => unreachable!(),
+                Err(e) => return Err(e)
             }
-            Some(1) => Some(buf[0]),
-            Some(_) => unreachable!(),
-            None => None
         }
     }
 
     /// Reads `len` bytes and appends them to a vector.
     ///
     /// May push fewer than the requested number of bytes on error
-    /// or EOF. Returns true on success, false on EOF or error.
-    ///
-    /// # Failure
-    ///
-    /// Raises the same conditions as `read`. Additionally raises `io_error`
-    /// on EOF. If `io_error` is handled then `push_bytes` may push less
-    /// than the requested number of bytes.
-    fn push_bytes(&mut self, buf: &mut ~[u8], len: uint) {
-        unsafe {
-            let start_len = buf.len();
-            let mut total_read = 0;
-
-            buf.reserve_additional(len);
-            buf.set_len(start_len + len);
-
-            (|| {
-                while total_read < len {
-                    let len = buf.len();
-                    let slice = buf.mut_slice(start_len + total_read, len);
-                    match self.read(slice) {
-                        Some(nread) => {
-                            total_read += nread;
-                        }
-                        None => {
-                            io_error::cond.raise(standard_error(EndOfFile));
-                            break;
-                        }
+    /// or EOF. If `Ok(())` is returned, then all of the requested bytes were
+    /// pushed on to the vector, otherwise the amount `len` bytes couldn't be
+    /// read (an error was encountered), and the error is returned.
+    fn push_bytes(&mut self, buf: &mut ~[u8], len: uint) -> IoResult<()> {
+        let start_len = buf.len();
+        let mut total_read = 0;
+
+        buf.reserve_additional(len);
+        unsafe { buf.set_len(start_len + len); }
+
+        (|| {
+            while total_read < len {
+                let len = buf.len();
+                let slice = buf.mut_slice(start_len + total_read, len);
+                match self.read(slice) {
+                    Ok(nread) => {
+                        total_read += nread;
                     }
+                    Err(e) => return Err(e)
                 }
-            }).finally(|| buf.set_len(start_len + total_read))
-        }
+            }
+            Ok(())
+        }).finally(|| unsafe { buf.set_len(start_len + total_read) })
     }
 
     /// Reads `len` bytes and gives you back a new vector of length `len`
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// Raises the same conditions as `read`. Additionally raises `io_error`
-    /// on EOF. If `io_error` is handled then the returned vector may
-    /// contain less than the requested number of bytes.
-    fn read_bytes(&mut self, len: uint) -> ~[u8] {
+    /// Fails with the same conditions as `read`. Additionally returns error on
+    /// on EOF. Note that if an error is returned, then some number of bytes may
+    /// have already been consumed from the underlying reader, and they are lost
+    /// (not returned as part of the error). If this is unacceptable, then it is
+    /// recommended to use the `push_bytes` or `read` methods.
+    fn read_bytes(&mut self, len: uint) -> IoResult<~[u8]> {
         let mut buf = vec::with_capacity(len);
-        self.push_bytes(&mut buf, len);
-        return buf;
+        match self.push_bytes(&mut buf, len) {
+            Ok(()) => Ok(buf),
+            Err(e) => Err(e),
+        }
     }
 
     /// Reads all remaining bytes from the stream.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// Raises the same conditions as the `read` method except for
-    /// `EndOfFile` which is swallowed.
-    fn read_to_end(&mut self) -> ~[u8] {
+    /// Returns any non-EOF error immediately. Previously read bytes are
+    /// discarded when an error is returned.
+    ///
+    /// When EOF is encountered, all bytes read up to that point are returned.
+    fn read_to_end(&mut self) -> IoResult<~[u8]> {
         let mut buf = vec::with_capacity(DEFAULT_BUF_SIZE);
-        let mut keep_reading = true;
-        io_error::cond.trap(|e| {
-            if e.kind == EndOfFile {
-                keep_reading = false;
-            } else {
-                io_error::cond.raise(e)
-            }
-        }).inside(|| {
-            while keep_reading {
-                self.push_bytes(&mut buf, DEFAULT_BUF_SIZE)
+        loop {
+            match self.push_bytes(&mut buf, DEFAULT_BUF_SIZE) {
+                Ok(()) => {}
+                Err(ref e) if e.kind == EndOfFile => break,
+                Err(e) => return Err(e)
             }
-        });
-        return buf;
+        }
+        return Ok(buf);
     }
 
     /// Reads all of the remaining bytes of this stream, interpreting them as a
     /// UTF-8 encoded stream. The corresponding string is returned.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise all the same conditions as the `read` method,
-    /// along with raising a condition if the input is not valid UTF-8.
-    fn read_to_str(&mut self) -> ~str {
-        match str::from_utf8_owned(self.read_to_end()) {
-            Some(s) => s,
-            None => {
-                io_error::cond.raise(standard_error(InvalidInput));
-                ~""
+    /// This function returns all of the same errors as `read_to_end` with an
+    /// additional error if the reader's contents are not a valid sequence of
+    /// UTF-8 bytes.
+    fn read_to_str(&mut self) -> IoResult<~str> {
+        self.read_to_end().and_then(|s| {
+            match str::from_utf8_owned(s) {
+                Some(s) => Ok(s),
+                None => Err(standard_error(InvalidInput)),
             }
-        }
+        })
     }
 
     /// Create an iterator that reads a single byte on
     /// each iteration, until EOF.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// Raises the same conditions as the `read` method, for
-    /// each call to its `.next()` method.
-    /// Ends the iteration if the condition is handled.
+    /// The iterator protocol causes all specifics about errors encountered to
+    /// be swallowed. All errors will be signified by returning `None` from the
+    /// iterator. If this is undesirable, it is recommended to use the
+    /// `read_byte` method.
     fn bytes<'r>(&'r mut self) -> extensions::Bytes<'r, Self> {
         extensions::Bytes::new(self)
     }
@@ -633,225 +566,219 @@ pub trait Reader {
     /// Reads `n` little-endian unsigned integer bytes.
     ///
     /// `n` must be between 1 and 8, inclusive.
-    fn read_le_uint_n(&mut self, nbytes: uint) -> u64 {
+    fn read_le_uint_n(&mut self, nbytes: uint) -> IoResult<u64> {
         assert!(nbytes > 0 && nbytes <= 8);
 
         let mut val = 0u64;
         let mut pos = 0;
         let mut i = nbytes;
         while i > 0 {
-            val += (self.read_u8() as u64) << pos;
+            val += (if_ok!(self.read_u8()) as u64) << pos;
             pos += 8;
             i -= 1;
         }
-        val
+        Ok(val)
     }
 
     /// Reads `n` little-endian signed integer bytes.
     ///
     /// `n` must be between 1 and 8, inclusive.
-    fn read_le_int_n(&mut self, nbytes: uint) -> i64 {
-        extend_sign(self.read_le_uint_n(nbytes), nbytes)
+    fn read_le_int_n(&mut self, nbytes: uint) -> IoResult<i64> {
+        self.read_le_uint_n(nbytes).map(|i| extend_sign(i, nbytes))
     }
 
     /// Reads `n` big-endian unsigned integer bytes.
     ///
     /// `n` must be between 1 and 8, inclusive.
-    fn read_be_uint_n(&mut self, nbytes: uint) -> u64 {
+    fn read_be_uint_n(&mut self, nbytes: uint) -> IoResult<u64> {
         assert!(nbytes > 0 && nbytes <= 8);
 
         let mut val = 0u64;
         let mut i = nbytes;
         while i > 0 {
             i -= 1;
-            val += (self.read_u8() as u64) << i * 8;
+            val += (if_ok!(self.read_u8()) as u64) << i * 8;
         }
-        val
+        Ok(val)
     }
 
     /// Reads `n` big-endian signed integer bytes.
     ///
     /// `n` must be between 1 and 8, inclusive.
-    fn read_be_int_n(&mut self, nbytes: uint) -> i64 {
-        extend_sign(self.read_be_uint_n(nbytes), nbytes)
+    fn read_be_int_n(&mut self, nbytes: uint) -> IoResult<i64> {
+        self.read_be_uint_n(nbytes).map(|i| extend_sign(i, nbytes))
     }
 
     /// Reads a little-endian unsigned integer.
     ///
     /// The number of bytes returned is system-dependant.
-    fn read_le_uint(&mut self) -> uint {
-        self.read_le_uint_n(uint::BYTES) as uint
+    fn read_le_uint(&mut self) -> IoResult<uint> {
+        self.read_le_uint_n(uint::BYTES).map(|i| i as uint)
     }
 
     /// Reads a little-endian integer.
     ///
     /// The number of bytes returned is system-dependant.
-    fn read_le_int(&mut self) -> int {
-        self.read_le_int_n(int::BYTES) as int
+    fn read_le_int(&mut self) -> IoResult<int> {
+        self.read_le_int_n(int::BYTES).map(|i| i as int)
     }
 
     /// Reads a big-endian unsigned integer.
     ///
     /// The number of bytes returned is system-dependant.
-    fn read_be_uint(&mut self) -> uint {
-        self.read_be_uint_n(uint::BYTES) as uint
+    fn read_be_uint(&mut self) -> IoResult<uint> {
+        self.read_be_uint_n(uint::BYTES).map(|i| i as uint)
     }
 
     /// Reads a big-endian integer.
     ///
     /// The number of bytes returned is system-dependant.
-    fn read_be_int(&mut self) -> int {
-        self.read_be_int_n(int::BYTES) as int
+    fn read_be_int(&mut self) -> IoResult<int> {
+        self.read_be_int_n(int::BYTES).map(|i| i as int)
     }
 
     /// Reads a big-endian `u64`.
     ///
     /// `u64`s are 8 bytes long.
-    fn read_be_u64(&mut self) -> u64 {
+    fn read_be_u64(&mut self) -> IoResult<u64> {
         self.read_be_uint_n(8)
     }
 
     /// Reads a big-endian `u32`.
     ///
     /// `u32`s are 4 bytes long.
-    fn read_be_u32(&mut self) -> u32 {
-        self.read_be_uint_n(4) as u32
+    fn read_be_u32(&mut self) -> IoResult<u32> {
+        self.read_be_uint_n(4).map(|i| i as u32)
     }
 
     /// Reads a big-endian `u16`.
     ///
     /// `u16`s are 2 bytes long.
-    fn read_be_u16(&mut self) -> u16 {
-        self.read_be_uint_n(2) as u16
+    fn read_be_u16(&mut self) -> IoResult<u16> {
+        self.read_be_uint_n(2).map(|i| i as u16)
     }
 
     /// Reads a big-endian `i64`.
     ///
     /// `i64`s are 8 bytes long.
-    fn read_be_i64(&mut self) -> i64 {
+    fn read_be_i64(&mut self) -> IoResult<i64> {
         self.read_be_int_n(8)
     }
 
     /// Reads a big-endian `i32`.
     ///
     /// `i32`s are 4 bytes long.
-    fn read_be_i32(&mut self) -> i32 {
-        self.read_be_int_n(4) as i32
+    fn read_be_i32(&mut self) -> IoResult<i32> {
+        self.read_be_int_n(4).map(|i| i as i32)
     }
 
     /// Reads a big-endian `i16`.
     ///
     /// `i16`s are 2 bytes long.
-    fn read_be_i16(&mut self) -> i16 {
-        self.read_be_int_n(2) as i16
+    fn read_be_i16(&mut self) -> IoResult<i16> {
+        self.read_be_int_n(2).map(|i| i as i16)
     }
 
     /// Reads a big-endian `f64`.
     ///
     /// `f64`s are 8 byte, IEEE754 double-precision floating point numbers.
-    fn read_be_f64(&mut self) -> f64 {
-        unsafe {
-            cast::transmute::<u64, f64>(self.read_be_u64())
-        }
+    fn read_be_f64(&mut self) -> IoResult<f64> {
+        self.read_be_u64().map(|i| unsafe {
+            cast::transmute::<u64, f64>(i)
+        })
     }
 
     /// Reads a big-endian `f32`.
     ///
     /// `f32`s are 4 byte, IEEE754 single-precision floating point numbers.
-    fn read_be_f32(&mut self) -> f32 {
-        unsafe {
-            cast::transmute::<u32, f32>(self.read_be_u32())
-        }
+    fn read_be_f32(&mut self) -> IoResult<f32> {
+        self.read_be_u32().map(|i| unsafe {
+            cast::transmute::<u32, f32>(i)
+        })
     }
 
     /// Reads a little-endian `u64`.
     ///
     /// `u64`s are 8 bytes long.
-    fn read_le_u64(&mut self) -> u64 {
+    fn read_le_u64(&mut self) -> IoResult<u64> {
         self.read_le_uint_n(8)
     }
 
     /// Reads a little-endian `u32`.
     ///
     /// `u32`s are 4 bytes long.
-    fn read_le_u32(&mut self) -> u32 {
-        self.read_le_uint_n(4) as u32
+    fn read_le_u32(&mut self) -> IoResult<u32> {
+        self.read_le_uint_n(4).map(|i| i as u32)
     }
 
     /// Reads a little-endian `u16`.
     ///
     /// `u16`s are 2 bytes long.
-    fn read_le_u16(&mut self) -> u16 {
-        self.read_le_uint_n(2) as u16
+    fn read_le_u16(&mut self) -> IoResult<u16> {
+        self.read_le_uint_n(2).map(|i| i as u16)
     }
 
     /// Reads a little-endian `i64`.
     ///
     /// `i64`s are 8 bytes long.
-    fn read_le_i64(&mut self) -> i64 {
+    fn read_le_i64(&mut self) -> IoResult<i64> {
         self.read_le_int_n(8)
     }
 
     /// Reads a little-endian `i32`.
     ///
     /// `i32`s are 4 bytes long.
-    fn read_le_i32(&mut self) -> i32 {
-        self.read_le_int_n(4) as i32
+    fn read_le_i32(&mut self) -> IoResult<i32> {
+        self.read_le_int_n(4).map(|i| i as i32)
     }
 
     /// Reads a little-endian `i16`.
     ///
     /// `i16`s are 2 bytes long.
-    fn read_le_i16(&mut self) -> i16 {
-        self.read_le_int_n(2) as i16
+    fn read_le_i16(&mut self) -> IoResult<i16> {
+        self.read_le_int_n(2).map(|i| i as i16)
     }
 
     /// Reads a little-endian `f64`.
     ///
     /// `f64`s are 8 byte, IEEE754 double-precision floating point numbers.
-    fn read_le_f64(&mut self) -> f64 {
-        unsafe {
-            cast::transmute::<u64, f64>(self.read_le_u64())
-        }
+    fn read_le_f64(&mut self) -> IoResult<f64> {
+        self.read_le_u64().map(|i| unsafe {
+            cast::transmute::<u64, f64>(i)
+        })
     }
 
     /// Reads a little-endian `f32`.
     ///
     /// `f32`s are 4 byte, IEEE754 single-precision floating point numbers.
-    fn read_le_f32(&mut self) -> f32 {
-        unsafe {
-            cast::transmute::<u32, f32>(self.read_le_u32())
-        }
+    fn read_le_f32(&mut self) -> IoResult<f32> {
+        self.read_le_u32().map(|i| unsafe {
+            cast::transmute::<u32, f32>(i)
+        })
     }
 
     /// Read a u8.
     ///
     /// `u8`s are 1 byte.
-    fn read_u8(&mut self) -> u8 {
-        match self.read_byte() {
-            Some(b) => b,
-            None => 0
-        }
+    fn read_u8(&mut self) -> IoResult<u8> {
+        self.read_byte()
     }
 
     /// Read an i8.
     ///
     /// `i8`s are 1 byte.
-    fn read_i8(&mut self) -> i8 {
-        match self.read_byte() {
-            Some(b) => b as i8,
-            None => 0
-        }
+    fn read_i8(&mut self) -> IoResult<i8> {
+        self.read_byte().map(|i| i as i8)
     }
 
 }
 
 impl Reader for ~Reader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.read(buf) }
 }
 
 impl<'a> Reader for &'a mut Reader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.read(buf) }
 }
 
 fn extend_sign(val: u64, nbytes: uint) -> i64 {
@@ -860,19 +787,22 @@ fn extend_sign(val: u64, nbytes: uint) -> i64 {
 }
 
 pub trait Writer {
-    /// Write the given buffer
+    /// Write the entirety of a given buffer
     ///
-    /// # Failure
+    /// # Errors
     ///
-    /// Raises the `io_error` condition on error
-    fn write(&mut self, buf: &[u8]);
+    /// If an error happens during the I/O operation, the error is returned as
+    /// `Err`. Note that it is considered an error if the entire buffer could
+    /// not be written, and if an error is returned then it is unknown how much
+    /// data (if any) was actually written.
+    fn write(&mut self, buf: &[u8]) -> IoResult<()>;
 
     /// Flush this output stream, ensuring that all intermediately buffered
     /// contents reach their destination.
     ///
     /// This is by default a no-op and implementers of the `Writer` trait should
     /// decide whether their stream needs to be buffered or not.
-    fn flush(&mut self) {}
+    fn flush(&mut self) -> IoResult<()> { Ok(()) }
 
     /// Write a rust string into this sink.
     ///
@@ -880,8 +810,8 @@ pub trait Writer {
     /// If other encodings are desired, it is recommended to compose this stream
     /// with another performing the conversion, or to use `write` with a
     /// converted byte-array instead.
-    fn write_str(&mut self, s: &str) {
-        self.write(s.as_bytes());
+    fn write_str(&mut self, s: &str) -> IoResult<()> {
+        self.write(s.as_bytes())
     }
 
     /// Writes a string into this sink, and then writes a literal newline (`\n`)
@@ -891,125 +821,124 @@ pub trait Writer {
     ///
     /// If other encodings or line ending flavors are desired, it is recommended
     /// that the `write` method is used specifically instead.
-    fn write_line(&mut self, s: &str) {
-        self.write_str(s);
-        self.write(['\n' as u8]);
+    fn write_line(&mut self, s: &str) -> IoResult<()> {
+        self.write_str(s).and_then(|()| self.write(['\n' as u8]))
     }
 
     /// Write a single char, encoded as UTF-8.
-    fn write_char(&mut self, c: char) {
+    fn write_char(&mut self, c: char) -> IoResult<()> {
         let mut buf = [0u8, ..4];
         let n = c.encode_utf8(buf.as_mut_slice());
-        self.write(buf.slice_to(n));
+        self.write(buf.slice_to(n))
     }
 
     /// Write the result of passing n through `int::to_str_bytes`.
-    fn write_int(&mut self, n: int) {
+    fn write_int(&mut self, n: int) -> IoResult<()> {
         int::to_str_bytes(n, 10u, |bytes| self.write(bytes))
     }
 
     /// Write the result of passing n through `uint::to_str_bytes`.
-    fn write_uint(&mut self, n: uint) {
+    fn write_uint(&mut self, n: uint) -> IoResult<()> {
         uint::to_str_bytes(n, 10u, |bytes| self.write(bytes))
     }
 
     /// Write a little-endian uint (number of bytes depends on system).
-    fn write_le_uint(&mut self, n: uint) {
+    fn write_le_uint(&mut self, n: uint) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, uint::BYTES, |v| self.write(v))
     }
 
     /// Write a little-endian int (number of bytes depends on system).
-    fn write_le_int(&mut self, n: int) {
+    fn write_le_int(&mut self, n: int) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, int::BYTES, |v| self.write(v))
     }
 
     /// Write a big-endian uint (number of bytes depends on system).
-    fn write_be_uint(&mut self, n: uint) {
+    fn write_be_uint(&mut self, n: uint) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, uint::BYTES, |v| self.write(v))
     }
 
     /// Write a big-endian int (number of bytes depends on system).
-    fn write_be_int(&mut self, n: int) {
+    fn write_be_int(&mut self, n: int) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, int::BYTES, |v| self.write(v))
     }
 
     /// Write a big-endian u64 (8 bytes).
-    fn write_be_u64(&mut self, n: u64) {
+    fn write_be_u64(&mut self, n: u64) -> IoResult<()> {
         extensions::u64_to_be_bytes(n, 8u, |v| self.write(v))
     }
 
     /// Write a big-endian u32 (4 bytes).
-    fn write_be_u32(&mut self, n: u32) {
+    fn write_be_u32(&mut self, n: u32) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, 4u, |v| self.write(v))
     }
 
     /// Write a big-endian u16 (2 bytes).
-    fn write_be_u16(&mut self, n: u16) {
+    fn write_be_u16(&mut self, n: u16) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, 2u, |v| self.write(v))
     }
 
     /// Write a big-endian i64 (8 bytes).
-    fn write_be_i64(&mut self, n: i64) {
+    fn write_be_i64(&mut self, n: i64) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, 8u, |v| self.write(v))
     }
 
     /// Write a big-endian i32 (4 bytes).
-    fn write_be_i32(&mut self, n: i32) {
+    fn write_be_i32(&mut self, n: i32) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, 4u, |v| self.write(v))
     }
 
     /// Write a big-endian i16 (2 bytes).
-    fn write_be_i16(&mut self, n: i16) {
+    fn write_be_i16(&mut self, n: i16) -> IoResult<()> {
         extensions::u64_to_be_bytes(n as u64, 2u, |v| self.write(v))
     }
 
     /// Write a big-endian IEEE754 double-precision floating-point (8 bytes).
-    fn write_be_f64(&mut self, f: f64) {
+    fn write_be_f64(&mut self, f: f64) -> IoResult<()> {
         unsafe {
             self.write_be_u64(cast::transmute(f))
         }
     }
 
     /// Write a big-endian IEEE754 single-precision floating-point (4 bytes).
-    fn write_be_f32(&mut self, f: f32) {
+    fn write_be_f32(&mut self, f: f32) -> IoResult<()> {
         unsafe {
             self.write_be_u32(cast::transmute(f))
         }
     }
 
     /// Write a little-endian u64 (8 bytes).
-    fn write_le_u64(&mut self, n: u64) {
+    fn write_le_u64(&mut self, n: u64) -> IoResult<()> {
         extensions::u64_to_le_bytes(n, 8u, |v| self.write(v))
     }
 
     /// Write a little-endian u32 (4 bytes).
-    fn write_le_u32(&mut self, n: u32) {
+    fn write_le_u32(&mut self, n: u32) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, 4u, |v| self.write(v))
     }
 
     /// Write a little-endian u16 (2 bytes).
-    fn write_le_u16(&mut self, n: u16) {
+    fn write_le_u16(&mut self, n: u16) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, 2u, |v| self.write(v))
     }
 
     /// Write a little-endian i64 (8 bytes).
-    fn write_le_i64(&mut self, n: i64) {
+    fn write_le_i64(&mut self, n: i64) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, 8u, |v| self.write(v))
     }
 
     /// Write a little-endian i32 (4 bytes).
-    fn write_le_i32(&mut self, n: i32) {
+    fn write_le_i32(&mut self, n: i32) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, 4u, |v| self.write(v))
     }
 
     /// Write a little-endian i16 (2 bytes).
-    fn write_le_i16(&mut self, n: i16) {
+    fn write_le_i16(&mut self, n: i16) -> IoResult<()> {
         extensions::u64_to_le_bytes(n as u64, 2u, |v| self.write(v))
     }
 
     /// Write a little-endian IEEE754 double-precision floating-point
     /// (8 bytes).
-    fn write_le_f64(&mut self, f: f64) {
+    fn write_le_f64(&mut self, f: f64) -> IoResult<()> {
         unsafe {
             self.write_le_u64(cast::transmute(f))
         }
@@ -1017,31 +946,31 @@ pub trait Writer {
 
     /// Write a little-endian IEEE754 single-precision floating-point
     /// (4 bytes).
-    fn write_le_f32(&mut self, f: f32) {
+    fn write_le_f32(&mut self, f: f32) -> IoResult<()> {
         unsafe {
             self.write_le_u32(cast::transmute(f))
         }
     }
 
     /// Write a u8 (1 byte).
-    fn write_u8(&mut self, n: u8) {
+    fn write_u8(&mut self, n: u8) -> IoResult<()> {
         self.write([n])
     }
 
     /// Write a i8 (1 byte).
-    fn write_i8(&mut self, n: i8) {
+    fn write_i8(&mut self, n: i8) -> IoResult<()> {
         self.write([n as u8])
     }
 }
 
 impl Writer for ~Writer {
-    fn write(&mut self, buf: &[u8]) { self.write(buf) }
-    fn flush(&mut self) { self.flush() }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.write(buf) }
+    fn flush(&mut self) -> IoResult<()> { self.flush() }
 }
 
 impl<'a> Writer for &'a mut Writer {
-    fn write(&mut self, buf: &[u8]) { self.write(buf) }
-    fn flush(&mut self) { self.flush() }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.write(buf) }
+    fn flush(&mut self) -> IoResult<()> { self.flush() }
 }
 
 pub trait Stream: Reader + Writer { }
@@ -1057,18 +986,18 @@ impl<T: Reader + Writer> Stream for T {}
 /// an iteration, but continue to yield elements if iteration
 /// is attempted again.
 ///
-/// # Failure
+/// # Error
 ///
-/// Raises the same conditions as the `read` method except for `EndOfFile`
-/// which is swallowed.
-/// Iteration yields `None` if the condition is handled.
+/// This iterator will swallow all I/O errors, transforming `Err` values to
+/// `None`. If errors need to be handled, it is recommended to use the
+/// `read_line` method directly.
 pub struct Lines<'r, T> {
     priv buffer: &'r mut T,
 }
 
 impl<'r, T: Buffer> Iterator<~str> for Lines<'r, T> {
     fn next(&mut self) -> Option<~str> {
-        self.buffer.read_line()
+        self.buffer.read_line().ok()
     }
 }
 
@@ -1085,11 +1014,12 @@ pub trait Buffer: Reader {
     /// consumed from this buffer returned to ensure that the bytes are never
     /// returned twice.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise on the `io_error` condition if a read error is
-    /// encountered.
-    fn fill<'a>(&'a mut self) -> &'a [u8];
+    /// This function will return an I/O error if the underlying reader was
+    /// read, but returned an error. Note that it is not an error to return a
+    /// 0-length buffer.
+    fn fill<'a>(&'a mut self) -> IoResult<&'a [u8]>;
 
     /// Tells this buffer that `amt` bytes have been consumed from the buffer,
     /// so they should no longer be returned in calls to `fill` or `read`.
@@ -1103,108 +1033,117 @@ pub trait Buffer: Reader {
     ///
     /// ```rust
     /// use std::io::{BufferedReader, stdin};
-    /// # let _g = ::std::io::ignore_io_error();
     ///
     /// let mut reader = BufferedReader::new(stdin());
     ///
-    /// let input = reader.read_line().unwrap_or(~"nothing");
+    /// let input = reader.read_line().ok().unwrap_or(~"nothing");
     /// ```
     ///
-    /// # Failure
+    /// # Error
+    ///
+    /// This function has the same error semantics as `read_until`:
+    ///
+    /// * All non-EOF errors will be returned immediately
+    /// * If an error is returned previously consumed bytes are lost
+    /// * EOF is only returned if no bytes have been read
+    /// * Reach EOF may mean that the delimiter is not present in the return
+    ///   value
     ///
-    /// This function will raise on the `io_error` condition (except for
-    /// `EndOfFile` which is swallowed) if a read error is encountered.
-    /// The task will also fail if sequence of bytes leading up to
-    /// the newline character are not valid UTF-8.
-    fn read_line(&mut self) -> Option<~str> {
-        self.read_until('\n' as u8).map(|line| str::from_utf8_owned(line).unwrap())
+    /// Additionally, this function can fail if the line of input read is not a
+    /// valid UTF-8 sequence of bytes.
+    fn read_line(&mut self) -> IoResult<~str> {
+        self.read_until('\n' as u8).and_then(|line|
+            match str::from_utf8_owned(line) {
+                Some(s) => Ok(s),
+                None => Err(standard_error(InvalidInput)),
+            }
+        )
     }
 
     /// Create an iterator that reads a line on each iteration until EOF.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// Iterator raises the same conditions as the `read` method
-    /// except for `EndOfFile`.
+    /// This iterator will transform all error values to `None`, discarding the
+    /// cause of the error. If this is undesirable, it is recommended to call
+    /// `read_line` directly.
     fn lines<'r>(&'r mut self) -> Lines<'r, Self> {
-        Lines {
-            buffer: self,
-        }
+        Lines { buffer: self }
     }
 
     /// Reads a sequence of bytes leading up to a specified delimiter. Once the
     /// specified byte is encountered, reading ceases and the bytes up to and
     /// including the delimiter are returned.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise on the `io_error` condition if a read error is
-    /// encountered, except that `EndOfFile` is swallowed.
-    fn read_until(&mut self, byte: u8) -> Option<~[u8]> {
+    /// If any I/O error is encountered other than EOF, the error is immediately
+    /// returned. Note that this may discard bytes which have already been read,
+    /// and those bytes will *not* be returned. It is recommended to use other
+    /// methods if this case is worrying.
+    ///
+    /// If EOF is encountered, then this function will return EOF if 0 bytes
+    /// have been read, otherwise the pending byte buffer is returned. This
+    /// is the reason that the byte buffer returned may not always contain the
+    /// delimiter.
+    fn read_until(&mut self, byte: u8) -> IoResult<~[u8]> {
         let mut res = ~[];
 
-        io_error::cond.trap(|e| {
-            if e.kind != EndOfFile {
-                io_error::cond.raise(e);
-            }
-        }).inside(|| {
-            let mut used;
-            loop {
-                {
-                    let available = self.fill();
-                    match available.iter().position(|&b| b == byte) {
-                        Some(i) => {
-                            res.push_all(available.slice_to(i + 1));
-                            used = i + 1;
-                            break
-                        }
-                        None => {
-                            res.push_all(available);
-                            used = available.len();
-                        }
+        let mut used;
+        loop {
+            {
+                let available = match self.fill() {
+                    Ok(n) => n,
+                    Err(ref e) if res.len() > 0 && e.kind == EndOfFile => {
+                        used = 0;
+                        break
+                    }
+                    Err(e) => return Err(e)
+                };
+                match available.iter().position(|&b| b == byte) {
+                    Some(i) => {
+                        res.push_all(available.slice_to(i + 1));
+                        used = i + 1;
+                        break
+                    }
+                    None => {
+                        res.push_all(available);
+                        used = available.len();
                     }
                 }
-                if used == 0 {
-                    break
-                }
-                self.consume(used);
             }
             self.consume(used);
-        });
-        return if res.len() == 0 {None} else {Some(res)};
-
+        }
+        self.consume(used);
+        Ok(res)
     }
 
     /// Reads the next utf8-encoded character from the underlying stream.
     ///
-    /// This will return `None` if the following sequence of bytes in the
-    /// stream are not a valid utf8-sequence, or if an I/O error is encountered.
-    ///
-    /// # Failure
-    ///
-    /// This function will raise on the `io_error` condition if a read error is
-    /// encountered.
-    fn read_char(&mut self) -> Option<char> {
-        let width = {
-            let available = self.fill();
-            if available.len() == 0 { return None } // read error
-            str::utf8_char_width(available[0])
-        };
-        if width == 0 { return None } // not uf8
-        let mut buf = [0, ..4];
+    /// # Error
+    ///
+    /// If an I/O error occurs, or EOF, then this function will return `Err`.
+    /// This function will also return error if the stream does not contain a
+    /// valid utf-8 encoded codepoint as the next few bytes in the stream.
+    fn read_char(&mut self) -> IoResult<char> {
+        let first_byte = if_ok!(self.read_byte());
+        let width = str::utf8_char_width(first_byte);
+        if width == 1 { return Ok(first_byte as char) }
+        if width == 0 { return Err(standard_error(InvalidInput)) } // not utf8
+        let mut buf = [first_byte, 0, 0, 0];
         {
-            let mut start = 0;
-            loop {
-                match self.read(buf.mut_slice(start, width)) {
-                    Some(n) if n == width - start => break,
-                    Some(n) if n < width - start => { start += n; }
-                    Some(..) | None => return None // read error
+            let mut start = 1;
+            while start < width {
+                match if_ok!(self.read(buf.mut_slice(start, width))) {
+                    n if n == width - start => break,
+                    n if n < width - start => { start += n; }
+                    _ => return Err(standard_error(InvalidInput)),
                 }
             }
         }
         match str::from_utf8(buf.slice_to(width)) {
-            Some(s) => Some(s.char_at(0)),
-            None => None
+            Some(s) => Ok(s.char_at(0)),
+            None => Err(standard_error(InvalidInput))
         }
     }
 }
@@ -1222,7 +1161,7 @@ pub enum SeekStyle {
 /// * Are `u64` and `i64` the right choices?
 pub trait Seek {
     /// Return position of file cursor in the stream
-    fn tell(&self) -> u64;
+    fn tell(&self) -> IoResult<u64>;
 
     /// Seek to an offset in a stream
     ///
@@ -1231,31 +1170,35 @@ pub trait Seek {
     /// # FIXME
     ///
     /// * What is the behavior when seeking past the end of a stream?
-    fn seek(&mut self, pos: i64, style: SeekStyle);
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()>;
 }
 
-/// A listener is a value that can consume itself to start listening for connections.
+/// A listener is a value that can consume itself to start listening for
+/// connections.
+///
 /// Doing so produces some sort of Acceptor.
 pub trait Listener<T, A: Acceptor<T>> {
     /// Spin up the listener and start queuing incoming connections
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// Raises `io_error` condition. If the condition is handled,
-    /// then `listen` returns `None`.
-    fn listen(self) -> Option<A>;
+    /// Returns `Err` if this listener could not be bound to listen for
+    /// connections. In all cases, this listener is consumed.
+    fn listen(self) -> IoResult<A>;
 }
 
 /// An acceptor is a value that presents incoming connections
 pub trait Acceptor<T> {
     /// Wait for and accept an incoming connection
     ///
-    /// # Failure
-    /// Raise `io_error` condition. If the condition is handled,
-    /// then `accept` returns `None`.
-    fn accept(&mut self) -> Option<T>;
+    /// # Error
+    ///
+    /// Returns `Err` if an I/O error is encountered.
+    fn accept(&mut self) -> IoResult<T>;
 
-    /// Create an iterator over incoming connection attempts
+    /// Create an iterator over incoming connection attempts.
+    ///
+    /// Note that I/O errors will be yielded by the iterator itself.
     fn incoming<'r>(&'r mut self) -> IncomingConnections<'r, Self> {
         IncomingConnections { inc: self }
     }
@@ -1264,23 +1207,22 @@ pub trait Acceptor<T> {
 /// An infinite iterator over incoming connection attempts.
 /// Calling `next` will block the task until a connection is attempted.
 ///
-/// Since connection attempts can continue forever, this iterator always returns Some.
-/// The Some contains another Option representing whether the connection attempt was succesful.
-/// A successful connection will be wrapped in Some.
-/// A failed connection is represented as a None and raises a condition.
+/// Since connection attempts can continue forever, this iterator always returns
+/// `Some`. The `Some` contains the `IoResult` representing whether the
+/// connection attempt was succesful.  A successful connection will be wrapped
+/// in `Ok`. A failed connection is represented as an `Err`.
 pub struct IncomingConnections<'a, A> {
     priv inc: &'a mut A,
 }
 
-impl<'a, T, A: Acceptor<T>> Iterator<Option<T>> for IncomingConnections<'a, A> {
-    fn next(&mut self) -> Option<Option<T>> {
+impl<'a, T, A: Acceptor<T>> Iterator<IoResult<T>> for IncomingConnections<'a, A> {
+    fn next(&mut self) -> Option<IoResult<T>> {
         Some(self.inc.accept())
     }
 }
 
 pub fn standard_error(kind: IoErrorKind) -> IoError {
     let desc = match kind {
-        PreviousIoError => "failing due to previous I/O error",
         EndOfFile => "end of file",
         IoUnavailable => "I/O is unavailable",
         InvalidInput => "invalid input",
@@ -1314,7 +1256,7 @@ pub enum FileMode {
 }
 
 /// Access permissions with which the file should be opened. `File`s
-/// opened with `Read` will raise an `io_error` condition if written to.
+/// opened with `Read` will return an error if written to.
 pub enum FileAccess {
     Read,
     Write,
diff --git a/src/libstd/io/net/addrinfo.rs b/src/libstd/io/net/addrinfo.rs
index 29bf6261a07..e9ffe97f1c3 100644
--- a/src/libstd/io/net/addrinfo.rs
+++ b/src/libstd/io/net/addrinfo.rs
@@ -17,8 +17,9 @@ getaddrinfo()
 
 */
 
-use option::{Option, Some, None};
+use io::IoResult;
 use io::net::ip::{SocketAddr, IpAddr};
+use option::{Option, Some, None};
 use rt::rtio::{IoFactory, LocalIo};
 use vec::ImmutableVector;
 
@@ -69,11 +70,7 @@ pub struct Info {
 
 /// Easy name resolution. Given a hostname, returns the list of IP addresses for
 /// that hostname.
-///
-/// # Failure
-///
-/// On failure, this will raise on the `io_error` condition.
-pub fn get_host_addresses(host: &str) -> Option<~[IpAddr]> {
+pub fn get_host_addresses(host: &str) -> IoResult<~[IpAddr]> {
     lookup(Some(host), None, None).map(|a| a.map(|i| i.address.ip))
 }
 
@@ -87,14 +84,10 @@ pub fn get_host_addresses(host: &str) -> Option<~[IpAddr]> {
 /// * hint - see the hint structure, and "man -s 3 getaddrinfo", for how this
 ///          controls lookup
 ///
-/// # Failure
-///
-/// On failure, this will raise on the `io_error` condition.
-///
 /// FIXME: this is not public because the `Hint` structure is not ready for public
 ///      consumption just yet.
 fn lookup(hostname: Option<&str>, servname: Option<&str>, hint: Option<Hint>)
-          -> Option<~[Info]> {
+          -> IoResult<~[Info]> {
     LocalIo::maybe_raise(|io| io.get_host_addresses(hostname, servname, hint))
 }
 
@@ -115,6 +108,6 @@ mod test {
     iotest!(fn issue_10663() {
         // Something should happen here, but this certainly shouldn't cause
         // everything to die. The actual outcome we don't care too much about.
-        get_host_addresses("example.com");
+        get_host_addresses("example.com").unwrap();
     } #[ignore])
 }
diff --git a/src/libstd/io/net/tcp.rs b/src/libstd/io/net/tcp.rs
index 475e3b206f2..a0bdc193d98 100644
--- a/src/libstd/io/net/tcp.rs
+++ b/src/libstd/io/net/tcp.rs
@@ -8,11 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use option::{Option, Some, None};
-use result::{Ok, Err};
 use io::net::ip::SocketAddr;
-use io::{Reader, Writer, Listener, Acceptor};
-use io::{io_error, EndOfFile};
+use io::{Reader, Writer, Listener, Acceptor, IoResult};
 use rt::rtio::{IoFactory, LocalIo, RtioSocket, RtioTcpListener};
 use rt::rtio::{RtioTcpAcceptor, RtioTcpStream};
 
@@ -25,57 +22,27 @@ impl TcpStream {
         TcpStream { obj: s }
     }
 
-    pub fn connect(addr: SocketAddr) -> Option<TcpStream> {
+    pub fn connect(addr: SocketAddr) -> IoResult<TcpStream> {
         LocalIo::maybe_raise(|io| {
             io.tcp_connect(addr).map(TcpStream::new)
         })
     }
 
-    pub fn peer_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.peer_name() {
-            Ok(pn) => Some(pn),
-            Err(ioerr) => {
-                debug!("failed to get peer name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn peer_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.peer_name()
     }
 
-    pub fn socket_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.socket_name() {
-            Ok(sn) => Some(sn),
-            Err(ioerr) => {
-                debug!("failed to get socket name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn socket_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.socket_name()
     }
 }
 
 impl Reader for TcpStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match self.obj.read(buf) {
-            Ok(read) => Some(read),
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                return None;
-            }
-        }
-    }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.obj.read(buf) }
 }
 
 impl Writer for TcpStream {
-    fn write(&mut self, buf: &[u8]) {
-        match self.obj.write(buf) {
-            Ok(_) => (),
-            Err(ioerr) => io_error::cond.raise(ioerr),
-        }
-    }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.obj.write(buf) }
 }
 
 pub struct TcpListener {
@@ -83,33 +50,20 @@ pub struct TcpListener {
 }
 
 impl TcpListener {
-    pub fn bind(addr: SocketAddr) -> Option<TcpListener> {
+    pub fn bind(addr: SocketAddr) -> IoResult<TcpListener> {
         LocalIo::maybe_raise(|io| {
             io.tcp_bind(addr).map(|l| TcpListener { obj: l })
         })
     }
 
-    pub fn socket_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.socket_name() {
-            Ok(sn) => Some(sn),
-            Err(ioerr) => {
-                debug!("failed to get socket name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn socket_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.socket_name()
     }
 }
 
 impl Listener<TcpStream, TcpAcceptor> for TcpListener {
-    fn listen(self) -> Option<TcpAcceptor> {
-        match self.obj.listen() {
-            Ok(acceptor) => Some(TcpAcceptor { obj: acceptor }),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn listen(self) -> IoResult<TcpAcceptor> {
+        self.obj.listen().map(|acceptor| TcpAcceptor { obj: acceptor })
     }
 }
 
@@ -118,14 +72,8 @@ pub struct TcpAcceptor {
 }
 
 impl Acceptor<TcpStream> for TcpAcceptor {
-    fn accept(&mut self) -> Option<TcpStream> {
-        match self.obj.accept() {
-            Ok(s) => Some(TcpStream::new(s)),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn accept(&mut self) -> IoResult<TcpStream> {
+        self.obj.accept().map(TcpStream::new)
     }
 }
 
@@ -138,29 +86,19 @@ mod test {
 
     // FIXME #11530 this fails on android because tests are run as root
     iotest!(fn bind_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert!(e.kind == PermissionDenied);
-            called = true;
-        }).inside(|| {
-            let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
-            let listener = TcpListener::bind(addr);
-            assert!(listener.is_none());
-        });
-        assert!(called);
+        let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
+        match TcpListener::bind(addr) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, PermissionDenied),
+        }
     } #[ignore(cfg(windows))] #[ignore(cfg(target_os = "android"))])
 
     iotest!(fn connect_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert_eq!(e.kind, ConnectionRefused);
-            called = true;
-        }).inside(|| {
-            let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
-            let stream = TcpStream::connect(addr);
-            assert!(stream.is_none());
-        });
-        assert!(called);
+        let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
+        match TcpStream::connect(addr) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, ConnectionRefused),
+        }
     })
 
     iotest!(fn smoke_test_ip4() {
@@ -170,14 +108,14 @@ mod test {
         spawn(proc() {
             port.recv();
             let mut stream = TcpStream::connect(addr);
-            stream.write([99]);
+            stream.write([99]).unwrap();
         });
 
         let mut acceptor = TcpListener::bind(addr).listen();
         chan.send(());
         let mut stream = acceptor.accept();
         let mut buf = [0];
-        stream.read(buf);
+        stream.read(buf).unwrap();
         assert!(buf[0] == 99);
     })
 
@@ -188,14 +126,14 @@ mod test {
         spawn(proc() {
             port.recv();
             let mut stream = TcpStream::connect(addr);
-            stream.write([99]);
+            stream.write([99]).unwrap();
         });
 
         let mut acceptor = TcpListener::bind(addr).listen();
         chan.send(());
         let mut stream = acceptor.accept();
         let mut buf = [0];
-        stream.read(buf);
+        stream.read(buf).unwrap();
         assert!(buf[0] == 99);
     })
 
@@ -214,7 +152,7 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
+        assert!(nread.is_err());
     })
 
     iotest!(fn read_eof_ip6() {
@@ -232,7 +170,7 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
+        assert!(nread.is_err());
     })
 
     iotest!(fn read_eof_twice_ip4() {
@@ -250,17 +188,15 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
-        io_error::cond.trap(|e| {
-            if cfg!(windows) {
-                assert_eq!(e.kind, NotConnected);
-            } else {
-                fail!();
+        assert!(nread.is_err());
+
+        match stream.read(buf) {
+            Ok(..) => fail!(),
+            Err(ref e) => {
+                assert!(e.kind == NotConnected || e.kind == EndOfFile,
+                        "unknown kind: {:?}", e.kind);
             }
-        }).inside(|| {
-            let nread = stream.read(buf);
-            assert!(nread.is_none());
-        })
+        }
     })
 
     iotest!(fn read_eof_twice_ip6() {
@@ -278,17 +214,15 @@ mod test {
         let mut stream = acceptor.accept();
         let mut buf = [0];
         let nread = stream.read(buf);
-        assert!(nread.is_none());
-        io_error::cond.trap(|e| {
-            if cfg!(windows) {
-                assert_eq!(e.kind, NotConnected);
-            } else {
-                fail!();
+        assert!(nread.is_err());
+
+        match stream.read(buf) {
+            Ok(..) => fail!(),
+            Err(ref e) => {
+                assert!(e.kind == NotConnected || e.kind == EndOfFile,
+                        "unknown kind: {:?}", e.kind);
             }
-        }).inside(|| {
-            let nread = stream.read(buf);
-            assert!(nread.is_none());
-        })
+        }
     })
 
     iotest!(fn write_close_ip4() {
@@ -306,19 +240,16 @@ mod test {
         let mut stream = acceptor.accept();
         let buf = [0];
         loop {
-            let mut stop = false;
-            io_error::cond.trap(|e| {
-                // NB: ECONNRESET on linux, EPIPE on mac, ECONNABORTED
-                //     on windows
-                assert!(e.kind == ConnectionReset ||
-                        e.kind == BrokenPipe ||
-                        e.kind == ConnectionAborted,
-                        "unknown error: {:?}", e);
-                stop = true;
-            }).inside(|| {
-                stream.write(buf);
-            });
-            if stop { break }
+            match stream.write(buf) {
+                Ok(..) => {}
+                Err(e) => {
+                    assert!(e.kind == ConnectionReset ||
+                            e.kind == BrokenPipe ||
+                            e.kind == ConnectionAborted,
+                            "unknown error: {:?}", e);
+                    break;
+                }
+            }
         }
     })
 
@@ -337,19 +268,16 @@ mod test {
         let mut stream = acceptor.accept();
         let buf = [0];
         loop {
-            let mut stop = false;
-            io_error::cond.trap(|e| {
-                // NB: ECONNRESET on linux, EPIPE on mac, ECONNABORTED
-                //     on windows
-                assert!(e.kind == ConnectionReset ||
-                        e.kind == BrokenPipe ||
-                        e.kind == ConnectionAborted,
-                        "unknown error: {:?}", e);
-                stop = true;
-            }).inside(|| {
-                stream.write(buf);
-            });
-            if stop { break }
+            match stream.write(buf) {
+                Ok(..) => {}
+                Err(e) => {
+                    assert!(e.kind == ConnectionReset ||
+                            e.kind == BrokenPipe ||
+                            e.kind == ConnectionAborted,
+                            "unknown error: {:?}", e);
+                    break;
+                }
+            }
         }
     })
 
@@ -362,7 +290,7 @@ mod test {
             port.recv();
             for _ in range(0, max) {
                 let mut stream = TcpStream::connect(addr);
-                stream.write([99]);
+                stream.write([99]).unwrap();
             }
         });
 
@@ -370,7 +298,7 @@ mod test {
         chan.send(());
         for ref mut stream in acceptor.incoming().take(max) {
             let mut buf = [0];
-            stream.read(buf);
+            stream.read(buf).unwrap();
             assert_eq!(buf[0], 99);
         }
     })
@@ -384,7 +312,7 @@ mod test {
             port.recv();
             for _ in range(0, max) {
                 let mut stream = TcpStream::connect(addr);
-                stream.write([99]);
+                stream.write([99]).unwrap();
             }
         });
 
@@ -392,7 +320,7 @@ mod test {
         chan.send(());
         for ref mut stream in acceptor.incoming().take(max) {
             let mut buf = [0];
-            stream.read(buf);
+            stream.read(buf).unwrap();
             assert_eq!(buf[0], 99);
         }
     })
@@ -410,7 +338,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == i as u8);
                     debug!("read");
                 });
@@ -429,7 +357,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([i as u8]);
+                stream.write([i as u8]).unwrap();
             });
         }
     })
@@ -447,7 +375,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == i as u8);
                     debug!("read");
                 });
@@ -466,7 +394,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([i as u8]);
+                stream.write([i as u8]).unwrap();
             });
         }
     })
@@ -484,7 +412,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == 99);
                     debug!("read");
                 });
@@ -503,7 +431,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([99]);
+                stream.write([99]).unwrap();
             });
         }
     })
@@ -521,7 +449,7 @@ mod test {
                 spawn(proc() {
                     let mut stream = stream;
                     let mut buf = [0];
-                    stream.read(buf);
+                    stream.read(buf).unwrap();
                     assert!(buf[0] == 99);
                     debug!("read");
                 });
@@ -540,7 +468,7 @@ mod test {
                 // Connect again before writing
                 connect(i + 1, addr);
                 debug!("writing");
-                stream.write([99]);
+                stream.write([99]).unwrap();
             });
         }
     })
@@ -551,7 +479,7 @@ mod test {
         // Make sure socket_name gives
         // us the socket we binded to.
         let so_name = listener.socket_name();
-        assert!(so_name.is_some());
+        assert!(so_name.is_ok());
         assert_eq!(addr, so_name.unwrap());
     }
 
@@ -561,20 +489,20 @@ mod test {
         spawn(proc() {
             let mut acceptor = TcpListener::bind(addr).listen();
             chan.send(());
-            acceptor.accept();
+            acceptor.accept().unwrap();
         });
 
         port.recv();
         let stream = TcpStream::connect(addr);
 
-        assert!(stream.is_some());
+        assert!(stream.is_ok());
         let mut stream = stream.unwrap();
 
         // Make sure peer_name gives us the
         // address/port of the peer we've
         // connected to.
         let peer_name = stream.peer_name();
-        assert!(peer_name.is_some());
+        assert!(peer_name.is_ok());
         assert_eq!(addr, peer_name.unwrap());
     }
 
@@ -593,37 +521,33 @@ mod test {
         let addr = next_test_ip4();
         let (p, c) = Chan::new();
         spawn(proc() {
-            let mut srv = TcpListener::bind(addr).listen();
+            let mut srv = TcpListener::bind(addr).listen().unwrap();
             c.send(());
             let mut cl = srv.accept().unwrap();
-            cl.write([10]);
+            cl.write([10]).unwrap();
             let mut b = [0];
-            cl.read(b);
+            cl.read(b).unwrap();
             c.send(());
         });
 
         p.recv();
         let mut c = TcpStream::connect(addr).unwrap();
         let mut b = [0, ..10];
-        assert_eq!(c.read(b), Some(1));
-        c.write([1]);
+        assert_eq!(c.read(b), Ok(1));
+        c.write([1]).unwrap();
         p.recv();
     })
 
     iotest!(fn double_bind() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert!(e.kind == ConnectionRefused || e.kind == OtherIoError);
-            called = true;
-        }).inside(|| {
-            let addr = next_test_ip4();
-            let listener = TcpListener::bind(addr).unwrap().listen();
-            assert!(listener.is_some());
-            let listener2 = TcpListener::bind(addr).and_then(|l|
-                                                    l.listen());
-            assert!(listener2.is_none());
-        });
-        assert!(called);
+        let addr = next_test_ip4();
+        let listener = TcpListener::bind(addr).unwrap().listen();
+        assert!(listener.is_ok());
+        match TcpListener::bind(addr).listen() {
+            Ok(..) => fail!(),
+            Err(e) => {
+                assert!(e.kind == ConnectionRefused || e.kind == OtherIoError);
+            }
+        }
     })
 
     iotest!(fn fast_rebind() {
@@ -632,7 +556,7 @@ mod test {
 
         spawn(proc() {
             port.recv();
-            let _stream = TcpStream::connect(addr);
+            let _stream = TcpStream::connect(addr).unwrap();
             // Close
             port.recv();
         });
@@ -641,7 +565,7 @@ mod test {
             let mut acceptor = TcpListener::bind(addr).listen();
             chan.send(());
             {
-                let _stream = acceptor.accept();
+                let _stream = acceptor.accept().unwrap();
                 // Close client
                 chan.send(());
             }
diff --git a/src/libstd/io/net/udp.rs b/src/libstd/io/net/udp.rs
index 1cf30d469f7..0ef62648afc 100644
--- a/src/libstd/io/net/udp.rs
+++ b/src/libstd/io/net/udp.rs
@@ -8,11 +8,9 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use option::{Option, Some, None};
 use result::{Ok, Err};
 use io::net::ip::SocketAddr;
-use io::{Reader, Writer};
-use io::{io_error, EndOfFile};
+use io::{Reader, Writer, IoResult};
 use rt::rtio::{RtioSocket, RtioUdpSocket, IoFactory, LocalIo};
 
 pub struct UdpSocket {
@@ -20,45 +18,26 @@ pub struct UdpSocket {
 }
 
 impl UdpSocket {
-    pub fn bind(addr: SocketAddr) -> Option<UdpSocket> {
+    pub fn bind(addr: SocketAddr) -> IoResult<UdpSocket> {
         LocalIo::maybe_raise(|io| {
             io.udp_bind(addr).map(|s| UdpSocket { obj: s })
         })
     }
 
-    pub fn recvfrom(&mut self, buf: &mut [u8]) -> Option<(uint, SocketAddr)> {
-        match self.obj.recvfrom(buf) {
-            Ok((nread, src)) => Some((nread, src)),
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                None
-            }
-        }
+    pub fn recvfrom(&mut self, buf: &mut [u8]) -> IoResult<(uint, SocketAddr)> {
+        self.obj.recvfrom(buf)
     }
 
-    pub fn sendto(&mut self, buf: &[u8], dst: SocketAddr) {
-        match self.obj.sendto(buf, dst) {
-            Ok(_) => (),
-            Err(ioerr) => io_error::cond.raise(ioerr),
-        }
+    pub fn sendto(&mut self, buf: &[u8], dst: SocketAddr) -> IoResult<()> {
+        self.obj.sendto(buf, dst)
     }
 
     pub fn connect(self, other: SocketAddr) -> UdpStream {
         UdpStream { socket: self, connectedTo: other }
     }
 
-    pub fn socket_name(&mut self) -> Option<SocketAddr> {
-        match self.obj.socket_name() {
-            Ok(sn) => Some(sn),
-            Err(ioerr) => {
-                debug!("failed to get socket name: {:?}", ioerr);
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    pub fn socket_name(&mut self) -> IoResult<SocketAddr> {
+        self.obj.socket_name()
     }
 }
 
@@ -76,21 +55,21 @@ impl UdpStream {
 }
 
 impl Reader for UdpStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let peer = self.connectedTo;
         self.as_socket(|sock| {
             match sock.recvfrom(buf) {
-                Some((_nread, src)) if src != peer => Some(0),
-                Some((nread, _src)) => Some(nread),
-                None => None,
+                Ok((_nread, src)) if src != peer => Ok(0),
+                Ok((nread, _src)) => Ok(nread),
+                Err(e) => Err(e),
             }
         })
     }
 }
 
 impl Writer for UdpStream {
-    fn write(&mut self, buf: &[u8]) {
-        self.as_socket(|sock| sock.sendto(buf, self.connectedTo));
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        self.as_socket(|sock| sock.sendto(buf, self.connectedTo))
     }
 }
 
@@ -101,16 +80,11 @@ mod test {
 
     // FIXME #11530 this fails on android because tests are run as root
     iotest!(fn bind_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert_eq!(e.kind, PermissionDenied);
-            called = true;
-        }).inside(|| {
-            let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
-            let socket = UdpSocket::bind(addr);
-            assert!(socket.is_none());
-        });
-        assert!(called);
+        let addr = SocketAddr { ip: Ipv4Addr(0, 0, 0, 0), port: 1 };
+        match UdpSocket::bind(addr) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, PermissionDenied),
+        }
     } #[ignore(cfg(windows))] #[ignore(cfg(target_os = "android"))])
 
     iotest!(fn socket_smoke_test_ip4() {
@@ -121,29 +95,29 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(ref mut client) => {
+                Ok(ref mut client) => {
                     port.recv();
-                    client.sendto([99], server_ip)
+                    client.sendto([99], server_ip).unwrap()
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
             chan2.send(());
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(ref mut server) => {
+            Ok(ref mut server) => {
                 chan.send(());
                 let mut buf = [0];
                 match server.recvfrom(buf) {
-                    Some((nread, src)) => {
+                    Ok((nread, src)) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                         assert_eq!(src, client_ip);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
         port2.recv();
     })
@@ -155,28 +129,28 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(ref mut client) => {
+                Ok(ref mut client) => {
                     port.recv();
-                    client.sendto([99], server_ip)
+                    client.sendto([99], server_ip).unwrap()
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(ref mut server) => {
+            Ok(ref mut server) => {
                 chan.send(());
                 let mut buf = [0];
                 match server.recvfrom(buf) {
-                    Some((nread, src)) => {
+                    Ok((nread, src)) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                         assert_eq!(src, client_ip);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
     })
 
@@ -188,32 +162,32 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(client) => {
+                Ok(client) => {
                     let client = ~client;
                     let mut stream = client.connect(server_ip);
                     port.recv();
-                    stream.write([99]);
+                    stream.write([99]).unwrap();
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
             chan2.send(());
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(server) => {
+            Ok(server) => {
                 let server = ~server;
                 let mut stream = server.connect(client_ip);
                 chan.send(());
                 let mut buf = [0];
                 match stream.read(buf) {
-                    Some(nread) => {
+                    Ok(nread) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
         port2.recv();
     })
@@ -226,32 +200,32 @@ mod test {
 
         spawn(proc() {
             match UdpSocket::bind(client_ip) {
-                Some(client) => {
+                Ok(client) => {
                     let client = ~client;
                     let mut stream = client.connect(server_ip);
                     port.recv();
-                    stream.write([99]);
+                    stream.write([99]).unwrap();
                 }
-                None => fail!()
+                Err(..) => fail!()
             }
             chan2.send(());
         });
 
         match UdpSocket::bind(server_ip) {
-            Some(server) => {
+            Ok(server) => {
                 let server = ~server;
                 let mut stream = server.connect(client_ip);
                 chan.send(());
                 let mut buf = [0];
                 match stream.read(buf) {
-                    Some(nread) => {
+                    Ok(nread) => {
                         assert_eq!(nread, 1);
                         assert_eq!(buf[0], 99);
                     }
-                    None => fail!()
+                    Err(..) => fail!()
                 }
             }
-            None => fail!()
+            Err(..) => fail!()
         }
         port2.recv();
     })
@@ -259,13 +233,13 @@ mod test {
     pub fn socket_name(addr: SocketAddr) {
         let server = UdpSocket::bind(addr);
 
-        assert!(server.is_some());
+        assert!(server.is_ok());
         let mut server = server.unwrap();
 
         // Make sure socket_name gives
         // us the socket we binded to.
         let so_name = server.socket_name();
-        assert!(so_name.is_some());
+        assert!(so_name.is_ok());
         assert_eq!(addr, so_name.unwrap());
     }
 
diff --git a/src/libstd/io/net/unix.rs b/src/libstd/io/net/unix.rs
index d470e9bfda1..ce95b987663 100644
--- a/src/libstd/io/net/unix.rs
+++ b/src/libstd/io/net/unix.rs
@@ -28,7 +28,7 @@ use c_str::ToCStr;
 use rt::rtio::{IoFactory, LocalIo, RtioUnixListener};
 use rt::rtio::{RtioUnixAcceptor, RtioPipe};
 use io::pipe::PipeStream;
-use io::{io_error, Listener, Acceptor, Reader, Writer};
+use io::{Listener, Acceptor, Reader, Writer, IoResult};
 
 /// A stream which communicates over a named pipe.
 pub struct UnixStream {
@@ -45,20 +45,17 @@ impl UnixStream {
     ///
     /// The returned stream will be closed when the object falls out of scope.
     ///
-    /// # Failure
-    ///
-    /// This function will raise on the `io_error` condition if the connection
-    /// could not be made.
-    ///
     /// # Example
     ///
-    ///     use std::io::net::unix::UnixStream;
+    /// ```rust
+    /// # #[allow(unused_must_use)];
+    /// use std::io::net::unix::UnixStream;
     ///
-    ///     let server = Path("path/to/my/socket");
-    ///     let mut stream = UnixStream::connect(&server);
-    ///     stream.write([1, 2, 3]);
-    ///
-    pub fn connect<P: ToCStr>(path: &P) -> Option<UnixStream> {
+    /// let server = Path::new("path/to/my/socket");
+    /// let mut stream = UnixStream::connect(&server);
+    /// stream.write([1, 2, 3]);
+    /// ```
+    pub fn connect<P: ToCStr>(path: &P) -> IoResult<UnixStream> {
         LocalIo::maybe_raise(|io| {
             io.unix_connect(&path.to_c_str()).map(UnixStream::new)
         })
@@ -66,11 +63,11 @@ impl UnixStream {
 }
 
 impl Reader for UnixStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> { self.obj.read(buf) }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.obj.read(buf) }
 }
 
 impl Writer for UnixStream {
-    fn write(&mut self, buf: &[u8]) { self.obj.write(buf) }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.obj.write(buf) }
 }
 
 pub struct UnixListener {
@@ -84,23 +81,20 @@ impl UnixListener {
     ///
     /// This listener will be closed when it falls out of scope.
     ///
-    /// # Failure
-    ///
-    /// This function will raise on the `io_error` condition if the specified
-    /// path could not be bound.
-    ///
     /// # Example
     ///
-    ///     use std::io::net::unix::UnixListener;
-    ///
-    ///     let server = Path("path/to/my/socket");
-    ///     let mut stream = UnixListener::bind(&server);
-    ///     for client in stream.incoming() {
-    ///         let mut client = client;
-    ///         client.write([1, 2, 3, 4]);
-    ///     }
+    /// ```
+    /// use std::io::net::unix::UnixListener;
+    /// use std::io::Listener;
     ///
-    pub fn bind<P: ToCStr>(path: &P) -> Option<UnixListener> {
+    /// let server = Path::new("path/to/my/socket");
+    /// let mut stream = UnixListener::bind(&server);
+    /// for client in stream.incoming() {
+    ///     let mut client = client;
+    ///     client.write([1, 2, 3, 4]);
+    /// }
+    /// ```
+    pub fn bind<P: ToCStr>(path: &P) -> IoResult<UnixListener> {
         LocalIo::maybe_raise(|io| {
             io.unix_bind(&path.to_c_str()).map(|s| UnixListener { obj: s })
         })
@@ -108,14 +102,8 @@ impl UnixListener {
 }
 
 impl Listener<UnixStream, UnixAcceptor> for UnixListener {
-    fn listen(self) -> Option<UnixAcceptor> {
-        match self.obj.listen() {
-            Ok(acceptor) => Some(UnixAcceptor { obj: acceptor }),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn listen(self) -> IoResult<UnixAcceptor> {
+        self.obj.listen().map(|obj| UnixAcceptor { obj: obj })
     }
 }
 
@@ -124,14 +112,8 @@ pub struct UnixAcceptor {
 }
 
 impl Acceptor<UnixStream> for UnixAcceptor {
-    fn accept(&mut self) -> Option<UnixStream> {
-        match self.obj.accept() {
-            Ok(s) => Some(UnixStream::new(s)),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-                None
-            }
-        }
+    fn accept(&mut self) -> IoResult<UnixStream> {
+        self.obj.accept().map(UnixStream::new)
     }
 }
 
@@ -159,39 +141,29 @@ mod tests {
 
     #[test]
     fn bind_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert!(e.kind == PermissionDenied);
-            called = true;
-        }).inside(|| {
-            let listener = UnixListener::bind(&("path/to/nowhere"));
-            assert!(listener.is_none());
-        });
-        assert!(called);
+        match UnixListener::bind(&("path/to/nowhere")) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, PermissionDenied),
+        }
     }
 
     #[test]
     fn connect_error() {
-        let mut called = false;
-        io_error::cond.trap(|e| {
-            assert_eq!(e.kind,
-                       if cfg!(windows) {OtherIoError} else {FileNotFound});
-            called = true;
-        }).inside(|| {
-            let stream = UnixStream::connect(&("path/to/nowhere"));
-            assert!(stream.is_none());
-        });
-        assert!(called);
+        match UnixStream::connect(&("path/to/nowhere")) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind,
+                        if cfg!(windows) {OtherIoError} else {FileNotFound})
+        }
     }
 
     #[test]
     fn smoke() {
         smalltest(proc(mut server) {
             let mut buf = [0];
-            server.read(buf);
+            server.read(buf).unwrap();
             assert!(buf[0] == 99);
         }, proc(mut client) {
-            client.write([99]);
+            client.write([99]).unwrap();
         })
     }
 
@@ -199,8 +171,8 @@ mod tests {
     fn read_eof() {
         smalltest(proc(mut server) {
             let mut buf = [0];
-            assert!(server.read(buf).is_none());
-            assert!(server.read(buf).is_none());
+            assert!(server.read(buf).is_err());
+            assert!(server.read(buf).is_err());
         }, proc(_client) {
             // drop the client
         })
@@ -210,15 +182,15 @@ mod tests {
     fn write_begone() {
         smalltest(proc(mut server) {
             let buf = [0];
-            let mut stop = false;
-            while !stop{
-                io_error::cond.trap(|e| {
-                    assert!(e.kind == BrokenPipe || e.kind == NotConnected,
-                            "unknown error {:?}", e);
-                    stop = true;
-                }).inside(|| {
-                    server.write(buf);
-                })
+            loop {
+                match server.write(buf) {
+                    Ok(..) => {}
+                    Err(e) => {
+                        assert!(e.kind == BrokenPipe || e.kind == NotConnected,
+                                "unknown error {:?}", e);
+                        break;
+                    }
+                }
             }
         }, proc(_client) {
             // drop the client
@@ -236,7 +208,7 @@ mod tests {
             port.recv();
             for _ in range(0, times) {
                 let mut stream = UnixStream::connect(&path2);
-                stream.write([100]);
+                stream.write([100]).unwrap();
             }
         });
 
@@ -245,7 +217,7 @@ mod tests {
         for _ in range(0, times) {
             let mut client = acceptor.accept();
             let mut buf = [0];
-            client.read(buf);
+            client.read(buf).unwrap();
             assert_eq!(buf[0], 100);
         }
     }
diff --git a/src/libstd/io/option.rs b/src/libstd/io/option.rs
deleted file mode 100644
index e2eec652d9d..00000000000
--- a/src/libstd/io/option.rs
+++ /dev/null
@@ -1,154 +0,0 @@
-// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
-// file at the top-level directory of this distribution and at
-// http://rust-lang.org/COPYRIGHT.
-//
-// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-// option. This file may not be copied, modified, or distributed
-// except according to those terms.
-
-//! Implementations of I/O traits for the Option type
-//!
-//! I/O constructors return option types to allow errors to be handled.
-//! These implementations allow e.g. `Option<File>` to be used
-//! as a `Reader` without unwrapping the option first.
-
-use option::*;
-use super::{Reader, Writer, Listener, Acceptor, Seek, SeekStyle};
-use super::{standard_error, PreviousIoError, io_error, IoError};
-
-fn prev_io_error() -> IoError {
-    standard_error(PreviousIoError)
-}
-
-impl<W: Writer> Writer for Option<W> {
-    fn write(&mut self, buf: &[u8]) {
-        match *self {
-            Some(ref mut writer) => writer.write(buf),
-            None => io_error::cond.raise(prev_io_error())
-        }
-    }
-
-    fn flush(&mut self) {
-        match *self {
-            Some(ref mut writer) => writer.flush(),
-            None => io_error::cond.raise(prev_io_error())
-        }
-    }
-}
-
-impl<R: Reader> Reader for Option<R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match *self {
-            Some(ref mut reader) => reader.read(buf),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                None
-            }
-        }
-    }
-}
-
-impl<S: Seek> Seek for Option<S> {
-    fn tell(&self) -> u64 {
-        match *self {
-            Some(ref seeker) => seeker.tell(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                0
-            }
-        }
-    }
-    fn seek(&mut self, pos: i64, style: SeekStyle) {
-        match *self {
-            Some(ref mut seeker) => seeker.seek(pos, style),
-            None => io_error::cond.raise(prev_io_error())
-        }
-    }
-}
-
-impl<T, A: Acceptor<T>, L: Listener<T, A>> Listener<T, A> for Option<L> {
-    fn listen(self) -> Option<A> {
-        match self {
-            Some(listener) => listener.listen(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                None
-            }
-        }
-    }
-}
-
-impl<T, A: Acceptor<T>> Acceptor<T> for Option<A> {
-    fn accept(&mut self) -> Option<T> {
-        match *self {
-            Some(ref mut acceptor) => acceptor.accept(),
-            None => {
-                io_error::cond.raise(prev_io_error());
-                None
-            }
-        }
-    }
-}
-
-#[cfg(test)]
-mod test {
-    use prelude::*;
-    use super::super::mem::*;
-    use super::super::{PreviousIoError, io_error};
-
-    #[test]
-    fn test_option_writer() {
-        let mut writer: Option<MemWriter> = Some(MemWriter::new());
-        writer.write([0, 1, 2]);
-        writer.flush();
-        assert_eq!(writer.unwrap().unwrap(), ~[0, 1, 2]);
-    }
-
-    #[test]
-    fn test_option_writer_error() {
-        let mut writer: Option<MemWriter> = None;
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            writer.write([0, 0, 0]);
-        });
-        assert!(called);
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            writer.flush();
-        });
-        assert!(called);
-    }
-
-    #[test]
-    fn test_option_reader() {
-        let mut reader: Option<MemReader> = Some(MemReader::new(~[0, 1, 2, 3]));
-        let mut buf = [0, 0];
-        reader.read(buf);
-        assert_eq!(buf, [0, 1]);
-    }
-
-    #[test]
-    fn test_option_reader_error() {
-        let mut reader: Option<MemReader> = None;
-        let mut buf = [];
-
-        let mut called = false;
-        io_error::cond.trap(|err| {
-            assert_eq!(err.kind, PreviousIoError);
-            called = true;
-        }).inside(|| {
-            reader.read(buf);
-        });
-        assert!(called);
-    }
-}
diff --git a/src/libstd/io/pipe.rs b/src/libstd/io/pipe.rs
index 9919d333f41..ca85707149b 100644
--- a/src/libstd/io/pipe.rs
+++ b/src/libstd/io/pipe.rs
@@ -14,7 +14,7 @@
 //! enough so that pipes can be created to child processes.
 
 use prelude::*;
-use io::{io_error, EndOfFile};
+use io::IoResult;
 use libc;
 use rt::rtio::{RtioPipe, LocalIo};
 
@@ -32,17 +32,15 @@ impl PipeStream {
     ///
     /// # Example
     ///
-    ///     use std::libc;
-    ///     use std::io::pipe;
+    /// ```rust
+    /// # #[allow(unused_must_use)];
+    /// use std::libc;
+    /// use std::io::pipe::PipeStream;
     ///
-    ///     let mut pipe = PipeStream::open(libc::STDERR_FILENO);
-    ///     pipe.write(bytes!("Hello, stderr!"));
-    ///
-    /// # Failure
-    ///
-    /// If the pipe cannot be created, an error will be raised on the
-    /// `io_error` condition.
-    pub fn open(fd: libc::c_int) -> Option<PipeStream> {
+    /// let mut pipe = PipeStream::open(libc::STDERR_FILENO);
+    /// pipe.write(bytes!("Hello, stderr!"));
+    /// ```
+    pub fn open(fd: libc::c_int) -> IoResult<PipeStream> {
         LocalIo::maybe_raise(|io| {
             io.pipe_open(fd).map(|obj| PipeStream { obj: obj })
         })
@@ -54,29 +52,11 @@ impl PipeStream {
 }
 
 impl Reader for PipeStream {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        match self.obj.read(buf) {
-            Ok(read) => Some(read),
-            Err(ioerr) => {
-                // EOF is indicated by returning None
-                if ioerr.kind != EndOfFile {
-                    io_error::cond.raise(ioerr);
-                }
-                return None;
-            }
-        }
-    }
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> { self.obj.read(buf) }
 }
 
 impl Writer for PipeStream {
-    fn write(&mut self, buf: &[u8]) {
-        match self.obj.write(buf) {
-            Ok(_) => (),
-            Err(ioerr) => {
-                io_error::cond.raise(ioerr);
-            }
-        }
-    }
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> { self.obj.write(buf) }
 }
 
 #[cfg(test)]
@@ -91,12 +71,12 @@ mod test {
         let (p, c) = Chan::new();
         spawn(proc() {
             let mut out = out;
-            out.write([10]);
+            out.write([10]).unwrap();
             p.recv(); // don't close the pipe until the other read has finished
         });
 
         let mut buf = [0, ..10];
-        input.read(buf);
+        input.read(buf).unwrap();
         c.send(());
     })
 }
diff --git a/src/libstd/io/process.rs b/src/libstd/io/process.rs
index 6a10f24916f..ccf3d4582de 100644
--- a/src/libstd/io/process.rs
+++ b/src/libstd/io/process.rs
@@ -14,7 +14,7 @@ use prelude::*;
 
 use libc;
 use io;
-use io::io_error;
+use io::IoResult;
 use rt::rtio::{RtioProcess, IoFactory, LocalIo};
 
 use fmt;
@@ -93,7 +93,7 @@ pub enum ProcessExit {
 
 impl fmt::Show for ProcessExit {
     /// Format a ProcessExit enum, to nicely present the information.
-    fn fmt(obj: &ProcessExit, f: &mut fmt::Formatter) {
+    fn fmt(obj: &ProcessExit, f: &mut fmt::Formatter) -> fmt::Result {
         match *obj {
             ExitStatus(code) =>  write!(f.buf, "exit code: {}", code),
             ExitSignal(code) =>  write!(f.buf, "signal: {}", code),
@@ -118,7 +118,7 @@ impl ProcessExit {
 impl Process {
     /// Creates a new pipe initialized, but not bound to any particular
     /// source/destination
-    pub fn new(config: ProcessConfig) -> Option<Process> {
+    pub fn new(config: ProcessConfig) -> IoResult<Process> {
         let mut config = Some(config);
         LocalIo::maybe_raise(|io| {
             io.spawn(config.take_unwrap()).map(|(p, io)| {
@@ -141,14 +141,9 @@ impl Process {
     /// Note that this is purely a wrapper around libuv's `uv_process_kill`
     /// function.
     ///
-    /// If the signal delivery fails, then the `io_error` condition is raised on
-    pub fn signal(&mut self, signal: int) {
-        match self.handle.kill(signal) {
-            Ok(()) => {}
-            Err(err) => {
-                io_error::cond.raise(err)
-            }
-        }
+    /// If the signal delivery fails, the corresponding error is returned.
+    pub fn signal(&mut self, signal: int) -> IoResult<()> {
+        self.handle.kill(signal)
     }
 
     /// Wait for the child to exit completely, returning the status that it
@@ -176,7 +171,6 @@ impl Drop for Process {
 mod tests {
     use io::process::{ProcessConfig, Process};
     use prelude::*;
-    use str;
 
     // FIXME(#10380)
     #[cfg(unix, not(target_os="android"))]
@@ -190,7 +184,7 @@ mod tests {
             io: io,
         };
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         assert!(p.wait().success());
     })
@@ -206,7 +200,7 @@ mod tests {
             cwd: None,
             io: io,
         };
-        match io::result(|| Process::new(args)) {
+        match Process::new(args) {
             Ok(..) => fail!(),
             Err(..) => {}
         }
@@ -224,7 +218,7 @@ mod tests {
             io: io,
         };
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         assert!(p.wait().matches_exit_status(1));
     })
@@ -240,7 +234,7 @@ mod tests {
             io: io,
         };
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         match p.wait() {
             process::ExitSignal(1) => {},
@@ -249,20 +243,12 @@ mod tests {
     })
 
     pub fn read_all(input: &mut Reader) -> ~str {
-        let mut ret = ~"";
-        let mut buf = [0, ..1024];
-        loop {
-            match input.read(buf) {
-                None => { break }
-                Some(n) => { ret.push_str(str::from_utf8(buf.slice_to(n)).unwrap()); }
-            }
-        }
-        return ret;
+        input.read_to_str().unwrap()
     }
 
     pub fn run_output(args: ProcessConfig) -> ~str {
         let p = Process::new(args);
-        assert!(p.is_some());
+        assert!(p.is_ok());
         let mut p = p.unwrap();
         assert!(p.io[0].is_none());
         assert!(p.io[1].is_some());
@@ -312,8 +298,8 @@ mod tests {
             cwd: None,
             io: io,
         };
-        let mut p = Process::new(args).expect("didn't create a proces?!");
-        p.io[0].get_mut_ref().write("foobar".as_bytes());
+        let mut p = Process::new(args).unwrap();
+        p.io[0].get_mut_ref().write("foobar".as_bytes()).unwrap();
         p.io[0] = None; // close stdin;
         let out = read_all(p.io[1].get_mut_ref() as &mut Reader);
         assert!(p.wait().success());
diff --git a/src/libstd/io/result.rs b/src/libstd/io/result.rs
new file mode 100644
index 00000000000..8e03cffd0fb
--- /dev/null
+++ b/src/libstd/io/result.rs
@@ -0,0 +1,128 @@
+// Copyright 2013 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Implementations of I/O traits for the IoResult type
+//!
+//! I/O constructors return option types to allow errors to be handled.
+//! These implementations allow e.g. `IoResult<File>` to be used
+//! as a `Reader` without unwrapping the result first.
+
+use clone::Clone;
+use result::{Ok, Err};
+use super::{Reader, Writer, Listener, Acceptor, Seek, SeekStyle, IoResult};
+
+impl<W: Writer> Writer for IoResult<W> {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        match *self {
+            Ok(ref mut writer) => writer.write(buf),
+            Err(ref e) => Err((*e).clone())
+        }
+    }
+
+    fn flush(&mut self) -> IoResult<()> {
+        match *self {
+            Ok(ref mut writer) => writer.flush(),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+}
+
+impl<R: Reader> Reader for IoResult<R> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
+        match *self {
+            Ok(ref mut reader) => reader.read(buf),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+}
+
+impl<S: Seek> Seek for IoResult<S> {
+    fn tell(&self) -> IoResult<u64> {
+        match *self {
+            Ok(ref seeker) => seeker.tell(),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+    fn seek(&mut self, pos: i64, style: SeekStyle) -> IoResult<()> {
+        match *self {
+            Ok(ref mut seeker) => seeker.seek(pos, style),
+            Err(ref e) => Err(e.clone())
+        }
+    }
+}
+
+impl<T, A: Acceptor<T>, L: Listener<T, A>> Listener<T, A> for IoResult<L> {
+    fn listen(self) -> IoResult<A> {
+        match self {
+            Ok(listener) => listener.listen(),
+            Err(e) => Err(e),
+        }
+    }
+}
+
+impl<T, A: Acceptor<T>> Acceptor<T> for IoResult<A> {
+    fn accept(&mut self) -> IoResult<T> {
+        match *self {
+            Ok(ref mut acceptor) => acceptor.accept(),
+            Err(ref e) => Err(e.clone()),
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use prelude::*;
+    use super::super::mem::*;
+    use io;
+
+    #[test]
+    fn test_option_writer() {
+        let mut writer: io::IoResult<MemWriter> = Ok(MemWriter::new());
+        writer.write([0, 1, 2]).unwrap();
+        writer.flush().unwrap();
+        assert_eq!(writer.unwrap().unwrap(), ~[0, 1, 2]);
+    }
+
+    #[test]
+    fn test_option_writer_error() {
+        let mut writer: io::IoResult<MemWriter> =
+            Err(io::standard_error(io::EndOfFile));
+
+        match writer.write([0, 0, 0]) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
+        match writer.flush() {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
+    }
+
+    #[test]
+    fn test_option_reader() {
+        let mut reader: io::IoResult<MemReader> =
+            Ok(MemReader::new(~[0, 1, 2, 3]));
+        let mut buf = [0, 0];
+        reader.read(buf).unwrap();
+        assert_eq!(buf, [0, 1]);
+    }
+
+    #[test]
+    fn test_option_reader_error() {
+        let mut reader: io::IoResult<MemReader> =
+            Err(io::standard_error(io::EndOfFile));
+        let mut buf = [];
+
+        match reader.read(buf) {
+            Ok(..) => fail!(),
+            Err(e) => assert_eq!(e.kind, io::EndOfFile),
+        }
+    }
+}
diff --git a/src/libstd/io/signal.rs b/src/libstd/io/signal.rs
index 5575e289b59..75804c40c58 100644
--- a/src/libstd/io/signal.rs
+++ b/src/libstd/io/signal.rs
@@ -20,10 +20,11 @@ definitions for a number of signals.
 */
 
 use clone::Clone;
+use result::{Ok, Err};
 use comm::{Port, SharedChan};
 use container::{Map, MutableMap};
 use hashmap;
-use option::{Some, None};
+use io;
 use rt::rtio::{IoFactory, LocalIo, RtioSignal};
 
 #[repr(int)]
@@ -112,23 +113,22 @@ impl Listener {
     /// a signal, and a later call to `recv` will return the signal that was
     /// received while no task was waiting on it.
     ///
-    /// # Failure
+    /// # Error
     ///
     /// If this function fails to register a signal handler, then an error will
-    /// be raised on the `io_error` condition and the function will return
-    /// false.
-    pub fn register(&mut self, signum: Signum) -> bool {
+    /// be returned.
+    pub fn register(&mut self, signum: Signum) -> io::IoResult<()> {
         if self.handles.contains_key(&signum) {
-            return true; // self is already listening to signum, so succeed
+            return Ok(()); // self is already listening to signum, so succeed
         }
         match LocalIo::maybe_raise(|io| {
             io.signal(signum, self.chan.clone())
         }) {
-            Some(handle) => {
+            Ok(handle) => {
                 self.handles.insert(signum, handle);
-                true
+                Ok(())
             }
-            None => false
+            Err(e) => Err(e)
         }
     }
 
@@ -159,7 +159,7 @@ mod test {
     #[test] #[cfg(unix, not(target_os="android"))] // FIXME(#10378)
     fn test_io_signal_smoketest() {
         let mut signal = Listener::new();
-        signal.register(Interrupt);
+        signal.register(Interrupt).unwrap();
         sigint();
         timer::sleep(10);
         match signal.port.recv() {
@@ -172,8 +172,8 @@ mod test {
     fn test_io_signal_two_signal_one_signum() {
         let mut s1 = Listener::new();
         let mut s2 = Listener::new();
-        s1.register(Interrupt);
-        s2.register(Interrupt);
+        s1.register(Interrupt).unwrap();
+        s2.register(Interrupt).unwrap();
         sigint();
         timer::sleep(10);
         match s1.port.recv() {
@@ -190,8 +190,8 @@ mod test {
     fn test_io_signal_unregister() {
         let mut s1 = Listener::new();
         let mut s2 = Listener::new();
-        s1.register(Interrupt);
-        s2.register(Interrupt);
+        s1.register(Interrupt).unwrap();
+        s2.register(Interrupt).unwrap();
         s2.unregister(Interrupt);
         sigint();
         timer::sleep(10);
@@ -203,15 +203,14 @@ mod test {
     fn test_io_signal_invalid_signum() {
         use io;
         use super::User1;
+        use result::{Ok, Err};
         let mut s = Listener::new();
         let mut called = false;
-        io::io_error::cond.trap(|_| {
-            called = true;
-        }).inside(|| {
-            if s.register(User1) {
+        match s.register(User1) {
+            Ok(..) => {
                 fail!("Unexpected successful registry of signum {:?}", User1);
             }
-        });
-        assert!(called);
+            Err(..) => {}
+        }
     }
 }
diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index d9fa2a4fc33..937ad0783e9 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -18,6 +18,7 @@ about the stream or terminal that it is attached to.
 # Example
 
 ```rust
+# #[allow(unused_must_use)];
 use std::io;
 
 let mut out = io::stdout();
@@ -28,7 +29,7 @@ out.write(bytes!("Hello, world!"));
 
 use container::Container;
 use fmt;
-use io::{Reader, Writer, io_error, IoError, OtherIoError,
+use io::{Reader, Writer, IoResult, IoError, OtherIoError,
          standard_error, EndOfFile, LineBufferedWriter};
 use libc;
 use option::{Option, Some, None};
@@ -114,7 +115,8 @@ fn reset_helper(w: ~Writer,
     match f(t.get(), w) {
         Some(mut w) => {
             drop(t);
-            w.flush();
+            // FIXME: is failing right here?
+            w.flush().unwrap();
             Some(w)
         }
         None => None
@@ -155,9 +157,9 @@ pub fn set_stderr(stderr: ~Writer) -> Option<~Writer> {
 //          // io1 aliases io2
 //      })
 //  })
-fn with_task_stdout(f: |&mut Writer|) {
+fn with_task_stdout(f: |&mut Writer| -> IoResult<()> ) {
     let task: Option<~Task> = Local::try_take();
-    match task {
+    let result = match task {
         Some(mut task) => {
             // Printing may run arbitrary code, so ensure that the task is in
             // TLS to allow all std services. Note that this means a print while
@@ -169,7 +171,7 @@ fn with_task_stdout(f: |&mut Writer|) {
             if my_stdout.is_none() {
                 my_stdout = Some(~LineBufferedWriter::new(stdout()) as ~Writer);
             }
-            f(*my_stdout.get_mut_ref());
+            let ret = f(*my_stdout.get_mut_ref());
 
             // Note that we need to be careful when putting the stdout handle
             // back into the task. If the handle was set to `Some` while
@@ -184,22 +186,29 @@ fn with_task_stdout(f: |&mut Writer|) {
             let prev = util::replace(&mut t.get().stdout, my_stdout);
             drop(t);
             drop(prev);
+            ret
         }
 
         None => {
             struct Stdout;
             impl Writer for Stdout {
-                fn write(&mut self, data: &[u8]) {
+                fn write(&mut self, data: &[u8]) -> IoResult<()> {
                     unsafe {
                         libc::write(libc::STDOUT_FILENO,
                                     data.as_ptr() as *libc::c_void,
                                     data.len() as libc::size_t);
                     }
+                    Ok(()) // just ignore the results
                 }
             }
             let mut io = Stdout;
-            f(&mut io as &mut Writer);
+            f(&mut io as &mut Writer)
         }
+    };
+
+    match result {
+        Ok(()) => {}
+        Err(e) => fail!("failed printing to stdout: {}", e),
     }
 }
 
@@ -226,8 +235,7 @@ pub fn print(s: &str) {
 /// `\n` character is printed to the console after the string.
 pub fn println(s: &str) {
     with_task_stdout(|io| {
-        io.write(s.as_bytes());
-        io.write(['\n' as u8]);
+        io.write(s.as_bytes()).and_then(|()| io.write(['\n' as u8]))
     })
 }
 
@@ -249,7 +257,7 @@ pub struct StdReader {
 }
 
 impl Reader for StdReader {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> IoResult<uint> {
         let ret = match self.inner {
             TTY(ref mut tty) => tty.read(buf),
             File(ref mut file) => file.read(buf).map(|i| i as uint),
@@ -260,15 +268,8 @@ impl Reader for StdReader {
             // return an actual EOF error, but apparently for stdin it's a
             // little different. Hence, here we convert a 0 length read to an
             // end-of-file indicator so the caller knows to stop reading.
-            Ok(0) => {
-                io_error::cond.raise(standard_error(EndOfFile));
-                None
-            }
-            Ok(amt) => Some(amt),
-            Err(e) => {
-                io_error::cond.raise(e);
-                None
-            }
+            Ok(0) => { Err(standard_error(EndOfFile)) }
+            ret @ Ok(..) | ret @ Err(..) => ret,
         }
     }
 }
@@ -283,30 +284,21 @@ impl StdWriter {
     /// when the writer is attached to something like a terminal, this is used
     /// to fetch the dimensions of the terminal.
     ///
-    /// If successful, returns Some((width, height)).
+    /// If successful, returns `Ok((width, height))`.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise on the `io_error` condition if an error
-    /// happens.
-    pub fn winsize(&mut self) -> Option<(int, int)> {
+    /// This function will return an error if the output stream is not actually
+    /// connected to a TTY instance, or if querying the TTY instance fails.
+    pub fn winsize(&mut self) -> IoResult<(int, int)> {
         match self.inner {
-            TTY(ref mut tty) => {
-                match tty.get_winsize() {
-                    Ok(p) => Some(p),
-                    Err(e) => {
-                        io_error::cond.raise(e);
-                        None
-                    }
-                }
-            }
+            TTY(ref mut tty) => tty.get_winsize(),
             File(..) => {
-                io_error::cond.raise(IoError {
+                Err(IoError {
                     kind: OtherIoError,
                     desc: "stream is not a tty",
                     detail: None,
-                });
-                None
+                })
             }
         }
     }
@@ -314,24 +306,19 @@ impl StdWriter {
     /// Controls whether this output stream is a "raw stream" or simply a normal
     /// stream.
     ///
-    /// # Failure
+    /// # Error
     ///
-    /// This function will raise on the `io_error` condition if an error
-    /// happens.
-    pub fn set_raw(&mut self, raw: bool) {
+    /// This function will return an error if the output stream is not actually
+    /// connected to a TTY instance, or if querying the TTY instance fails.
+    pub fn set_raw(&mut self, raw: bool) -> IoResult<()> {
         match self.inner {
-            TTY(ref mut tty) => {
-                match tty.set_raw(raw) {
-                    Ok(()) => {},
-                    Err(e) => io_error::cond.raise(e),
-                }
-            }
+            TTY(ref mut tty) => tty.set_raw(raw),
             File(..) => {
-                io_error::cond.raise(IoError {
+                Err(IoError {
                     kind: OtherIoError,
                     desc: "stream is not a tty",
                     detail: None,
-                });
+                })
             }
         }
     }
@@ -346,14 +333,10 @@ impl StdWriter {
 }
 
 impl Writer for StdWriter {
-    fn write(&mut self, buf: &[u8]) {
-        let ret = match self.inner {
+    fn write(&mut self, buf: &[u8]) -> IoResult<()> {
+        match self.inner {
             TTY(ref mut tty) => tty.write(buf),
             File(ref mut file) => file.write(buf),
-        };
-        match ret {
-            Ok(()) => {}
-            Err(e) => io_error::cond.raise(e)
         }
     }
 }
@@ -376,7 +359,7 @@ mod tests {
             set_stdout(~w as ~Writer);
             println!("hello!");
         });
-        assert_eq!(r.read_to_str(), ~"hello!\n");
+        assert_eq!(r.read_to_str().unwrap(), ~"hello!\n");
     })
 
     iotest!(fn capture_stderr() {
@@ -388,7 +371,7 @@ mod tests {
             set_stderr(~w as ~Writer);
             fail!("my special message");
         });
-        let s = r.read_to_str();
+        let s = r.read_to_str().unwrap();
         assert!(s.contains("my special message"));
     })
 }
diff --git a/src/libstd/io/timer.rs b/src/libstd/io/timer.rs
index 24eaf6adf3f..692aaa7afd0 100644
--- a/src/libstd/io/timer.rs
+++ b/src/libstd/io/timer.rs
@@ -39,8 +39,8 @@ loop {
 */
 
 use comm::Port;
-use option::Option;
 use rt::rtio::{IoFactory, LocalIo, RtioTimer};
+use io::IoResult;
 
 pub struct Timer {
     priv obj: ~RtioTimer
@@ -48,7 +48,8 @@ pub struct Timer {
 
 /// Sleep the current task for `msecs` milliseconds.
 pub fn sleep(msecs: u64) {
-    let mut timer = Timer::new().expect("timer::sleep: could not create a Timer");
+    let timer = Timer::new();
+    let mut timer = timer.ok().expect("timer::sleep: could not create a Timer");
 
     timer.sleep(msecs)
 }
@@ -57,7 +58,7 @@ impl Timer {
     /// Creates a new timer which can be used to put the current task to sleep
     /// for a number of milliseconds, or to possibly create channels which will
     /// get notified after an amount of time has passed.
-    pub fn new() -> Option<Timer> {
+    pub fn new() -> IoResult<Timer> {
         LocalIo::maybe_raise(|io| io.timer_init().map(|t| Timer { obj: t }))
     }
 
diff --git a/src/libstd/io/util.rs b/src/libstd/io/util.rs
index a1794d24fc9..c4d92b36ecf 100644
--- a/src/libstd/io/util.rs
+++ b/src/libstd/io/util.rs
@@ -7,8 +7,10 @@
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
+
 use prelude::*;
 use cmp;
+use io;
 use vec::bytes::MutableByteVector;
 
 /// Wraps a `Reader`, limiting the number of bytes that can be read from it.
@@ -25,9 +27,9 @@ impl<'a, R: Reader> LimitReader<'a, R> {
 }
 
 impl<'a, R: Reader> Reader for LimitReader<'a, R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
         if self.limit == 0 {
-            return None;
+            return Err(io::standard_error(io::EndOfFile));
         }
 
         let len = cmp::min(self.limit, buf.len());
@@ -43,7 +45,7 @@ pub struct NullWriter;
 
 impl Writer for NullWriter {
     #[inline]
-    fn write(&mut self, _buf: &[u8]) { }
+    fn write(&mut self, _buf: &[u8]) -> io::IoResult<()> { Ok(()) }
 }
 
 /// A `Reader` which returns an infinite stream of 0 bytes, like /dev/zero.
@@ -51,9 +53,9 @@ pub struct ZeroReader;
 
 impl Reader for ZeroReader {
     #[inline]
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
         buf.set_memory(0);
-        Some(buf.len())
+        Ok(buf.len())
     }
 }
 
@@ -62,8 +64,8 @@ pub struct NullReader;
 
 impl Reader for NullReader {
     #[inline]
-    fn read(&mut self, _buf: &mut [u8]) -> Option<uint> {
-        None
+    fn read(&mut self, _buf: &mut [u8]) -> io::IoResult<uint> {
+        Err(io::standard_error(io::EndOfFile))
     }
 }
 
@@ -81,17 +83,21 @@ impl MultiWriter {
 
 impl Writer for MultiWriter {
     #[inline]
-    fn write(&mut self, buf: &[u8]) {
+    fn write(&mut self, buf: &[u8]) -> io::IoResult<()> {
+        let mut ret = Ok(());
         for writer in self.writers.mut_iter() {
-            writer.write(buf);
+            ret = ret.and(writer.write(buf));
         }
+        return ret;
     }
 
     #[inline]
-    fn flush(&mut self) {
+    fn flush(&mut self) -> io::IoResult<()> {
+        let mut ret = Ok(());
         for writer in self.writers.mut_iter() {
-            writer.flush();
+            ret = ret.and(writer.flush());
         }
+        return ret;
     }
 }
 
@@ -111,20 +117,25 @@ impl<R: Reader, I: Iterator<R>> ChainedReader<I, R> {
 }
 
 impl<R: Reader, I: Iterator<R>> Reader for ChainedReader<I, R> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
         loop {
-            match self.cur_reader {
+            let err = match self.cur_reader {
                 Some(ref mut r) => {
                     match r.read(buf) {
-                        Some(len) => return Some(len),
-                        None => {}
+                        Ok(len) => return Ok(len),
+                        Err(ref e) if e.kind == io::EndOfFile => None,
+                        Err(e) => Some(e),
                     }
                 }
                 None => break
+            };
+            self.cur_reader = self.readers.next();
+            match err {
+                Some(e) => return Err(e),
+                None => {}
             }
-            self.cur_reader = self.readers.next()
         }
-        None
+        Err(io::standard_error(io::EndOfFile))
     }
 }
 
@@ -150,27 +161,29 @@ impl<R: Reader, W: Writer> TeeReader<R, W> {
 }
 
 impl<R: Reader, W: Writer> Reader for TeeReader<R, W> {
-    fn read(&mut self, buf: &mut [u8]) -> Option<uint> {
-        self.reader.read(buf).map(|len| {
-            self.writer.write(buf.slice_to(len));
-            len
+    fn read(&mut self, buf: &mut [u8]) -> io::IoResult<uint> {
+        self.reader.read(buf).and_then(|len| {
+            self.writer.write(buf.slice_to(len)).map(|()| len)
         })
     }
 }
 
 /// Copies all data from a `Reader` to a `Writer`.
-pub fn copy<R: Reader, W: Writer>(r: &mut R, w: &mut W) {
+pub fn copy<R: Reader, W: Writer>(r: &mut R, w: &mut W) -> io::IoResult<()> {
     let mut buf = [0, ..super::DEFAULT_BUF_SIZE];
     loop {
-        match r.read(buf) {
-            Some(len) => w.write(buf.slice_to(len)),
-            None => break
-        }
+        let len = match r.read(buf) {
+            Ok(len) => len,
+            Err(ref e) if e.kind == io::EndOfFile => return Ok(()),
+            Err(e) => return Err(e),
+        };
+        if_ok!(w.write(buf.slice_to(len)));
     }
 }
 
 #[cfg(test)]
 mod test {
+    use io;
     use io::{MemReader, MemWriter};
     use super::*;
     use prelude::*;
@@ -180,7 +193,7 @@ mod test {
         let mut r = MemReader::new(~[0, 1, 2]);
         {
             let mut r = LimitReader::new(&mut r, 4);
-            assert_eq!(~[0, 1, 2], r.read_to_end());
+            assert_eq!(~[0, 1, 2], r.read_to_end().unwrap());
         }
     }
 
@@ -189,24 +202,24 @@ mod test {
         let mut r = MemReader::new(~[0, 1, 2]);
         {
             let mut r = LimitReader::new(&mut r, 2);
-            assert_eq!(~[0, 1], r.read_to_end());
+            assert_eq!(~[0, 1], r.read_to_end().unwrap());
         }
-        assert_eq!(~[2], r.read_to_end());
+        assert_eq!(~[2], r.read_to_end().unwrap());
     }
 
     #[test]
     fn test_null_writer() {
         let mut s = NullWriter;
         let buf = ~[0, 0, 0];
-        s.write(buf);
-        s.flush();
+        s.write(buf).unwrap();
+        s.flush().unwrap();
     }
 
     #[test]
     fn test_zero_reader() {
         let mut s = ZeroReader;
         let mut buf = ~[1, 2, 3];
-        assert_eq!(s.read(buf), Some(3));
+        assert_eq!(s.read(buf), Ok(3));
         assert_eq!(~[0, 0, 0], buf);
     }
 
@@ -214,7 +227,7 @@ mod test {
     fn test_null_reader() {
         let mut r = NullReader;
         let mut buf = ~[0];
-        assert_eq!(r.read(buf), None);
+        assert!(r.read(buf).is_err());
     }
 
     #[test]
@@ -224,21 +237,23 @@ mod test {
 
         struct TestWriter;
         impl Writer for TestWriter {
-            fn write(&mut self, _buf: &[u8]) {
+            fn write(&mut self, _buf: &[u8]) -> io::IoResult<()> {
                 unsafe { writes += 1 }
+                Ok(())
             }
 
-            fn flush(&mut self) {
+            fn flush(&mut self) -> io::IoResult<()> {
                 unsafe { flushes += 1 }
+                Ok(())
             }
         }
 
         let mut multi = MultiWriter::new(~[~TestWriter as ~Writer,
                                            ~TestWriter as ~Writer]);
-        multi.write([1, 2, 3]);
+        multi.write([1, 2, 3]).unwrap();
         assert_eq!(2, unsafe { writes });
         assert_eq!(0, unsafe { flushes });
-        multi.flush();
+        multi.flush().unwrap();
         assert_eq!(2, unsafe { writes });
         assert_eq!(2, unsafe { flushes });
     }
@@ -248,14 +263,14 @@ mod test {
         let rs = ~[MemReader::new(~[0, 1]), MemReader::new(~[]),
                    MemReader::new(~[2, 3])];
         let mut r = ChainedReader::new(rs.move_iter());
-        assert_eq!(~[0, 1, 2, 3], r.read_to_end());
+        assert_eq!(~[0, 1, 2, 3], r.read_to_end().unwrap());
     }
 
     #[test]
     fn test_tee_reader() {
         let mut r = TeeReader::new(MemReader::new(~[0, 1, 2]),
                                    MemWriter::new());
-        assert_eq!(~[0, 1, 2], r.read_to_end());
+        assert_eq!(~[0, 1, 2], r.read_to_end().unwrap());
         let (_, w) = r.unwrap();
         assert_eq!(~[0, 1, 2], w.unwrap());
     }
@@ -264,7 +279,7 @@ mod test {
     fn test_copy() {
         let mut r = MemReader::new(~[0, 1, 2, 3, 4]);
         let mut w = MemWriter::new();
-        copy(&mut r, &mut w);
+        copy(&mut r, &mut w).unwrap();
         assert_eq!(~[0, 1, 2, 3, 4], w.unwrap());
     }
 }
diff --git a/src/libstd/logging.rs b/src/libstd/logging.rs
index 636d3ffd90a..c5e66ffc7be 100644
--- a/src/libstd/logging.rs
+++ b/src/libstd/logging.rs
@@ -102,6 +102,7 @@ use io::Writer;
 use ops::Drop;
 use option::{Some, None, Option};
 use prelude::drop;
+use result::{Ok, Err};
 use rt::local::Local;
 use rt::task::Task;
 use util;
@@ -131,13 +132,19 @@ struct DefaultLogger {
 impl Logger for DefaultLogger {
     // by default, just ignore the level
     fn log(&mut self, _level: u32, args: &fmt::Arguments) {
-        fmt::writeln(&mut self.handle, args);
+        match fmt::writeln(&mut self.handle, args) {
+            Err(e) => fail!("failed to log: {}", e),
+            Ok(()) => {}
+        }
     }
 }
 
 impl Drop for DefaultLogger {
     fn drop(&mut self) {
-        self.handle.flush();
+        match self.handle.flush() {
+            Err(e) => fail!("failed to flush a logger: {}", e),
+            Ok(()) => {}
+        }
     }
 }
 
diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 4032b63790b..b31ae92d742 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -197,3 +197,8 @@ macro_rules! local_data_key (
         pub static $name: ::std::local_data::Key<$ty> = &::std::local_data::Key;
     )
 )
+
+#[macro_export]
+macro_rules! if_ok (
+    ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
+)
diff --git a/src/libstd/option.rs b/src/libstd/option.rs
index 83cedd92a3f..19478e3dbb3 100644
--- a/src/libstd/option.rs
+++ b/src/libstd/option.rs
@@ -382,7 +382,7 @@ impl<T: Default> Option<T> {
 
 impl<T: fmt::Show> fmt::Show for Option<T> {
     #[inline]
-    fn fmt(s: &Option<T>, f: &mut fmt::Formatter) {
+    fn fmt(s: &Option<T>, f: &mut fmt::Formatter) -> fmt::Result {
         match *s {
             Some(ref t) => write!(f.buf, "Some({})", *t),
             None        => write!(f.buf, "None")
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 0ea1c7510a1..541db01f148 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -372,9 +372,9 @@ pub fn self_exe_name() -> Option<Path> {
     fn load_self() -> Option<~[u8]> {
         use std::io;
 
-        match io::result(|| io::fs::readlink(&Path::new("/proc/self/exe"))) {
-            Ok(Some(path)) => Some(path.as_vec().to_owned()),
-            Ok(None) | Err(..) => None
+        match io::fs::readlink(&Path::new("/proc/self/exe")) {
+            Ok(path) => Some(path.as_vec().to_owned()),
+            Err(..) => None
         }
     }
 
@@ -929,7 +929,7 @@ pub enum MapError {
 }
 
 impl fmt::Show for MapError {
-    fn fmt(val: &MapError, out: &mut fmt::Formatter) {
+    fn fmt(val: &MapError, out: &mut fmt::Formatter) -> fmt::Result {
         let str = match *val {
             ErrFdNotAvail => "fd not available for reading or writing",
             ErrInvalidFd => "Invalid fd",
@@ -944,23 +944,19 @@ impl fmt::Show for MapError {
             ErrAlreadyExists => "File mapping for specified file already exists",
             ErrZeroLength => "Zero-length mapping not allowed",
             ErrUnknown(code) => {
-                write!(out.buf, "Unknown error = {}", code);
-                return
+                return write!(out.buf, "Unknown error = {}", code)
             },
             ErrVirtualAlloc(code) => {
-                write!(out.buf, "VirtualAlloc failure = {}", code);
-                return
+                return write!(out.buf, "VirtualAlloc failure = {}", code)
             },
             ErrCreateFileMappingW(code) => {
-                format!("CreateFileMappingW failure = {}", code);
-                return
+                return write!(out.buf, "CreateFileMappingW failure = {}", code)
             },
             ErrMapViewOfFile(code) => {
-                write!(out.buf, "MapViewOfFile failure = {}", code);
-                return
+                return write!(out.buf, "MapViewOfFile failure = {}", code)
             }
         };
-        write!(out.buf, "{}", str);
+        write!(out.buf, "{}", str)
     }
 }
 
@@ -1496,7 +1492,6 @@ mod tests {
         use result::{Ok, Err};
         use os::*;
         use libc::*;
-        use io;
         use io::fs;
 
         #[cfg(unix)]
@@ -1540,9 +1535,9 @@ mod tests {
             assert!(*chunk.data == 0xbe);
             close(fd);
         }
+        drop(chunk);
 
-        let _guard = io::ignore_io_error();
-        fs::unlink(&path);
+        fs::unlink(&path).unwrap();
     }
 
     // More recursive_mkdir tests are in extra::tempfile
diff --git a/src/libstd/path/mod.rs b/src/libstd/path/mod.rs
index 86f96a1075b..4aa4a3feab1 100644
--- a/src/libstd/path/mod.rs
+++ b/src/libstd/path/mod.rs
@@ -533,7 +533,7 @@ pub struct Display<'a, P> {
 }
 
 impl<'a, P: GenericPath> fmt::Show for Display<'a, P> {
-    fn fmt(d: &Display<P>, f: &mut fmt::Formatter) {
+    fn fmt(d: &Display<P>, f: &mut fmt::Formatter) -> fmt::Result {
         d.with_str(|s| f.pad(s))
     }
 }
diff --git a/src/libstd/rand/os.rs b/src/libstd/rand/os.rs
index c359d79d275..e9068c6b0c8 100644
--- a/src/libstd/rand/os.rs
+++ b/src/libstd/rand/os.rs
@@ -62,7 +62,7 @@ impl OSRng {
     pub fn new() -> OSRng {
         use path::Path;
         let reader = File::open(&Path::new("/dev/urandom"));
-        let reader = reader.expect("Error opening /dev/urandom");
+        let reader = reader.ok().expect("Error opening /dev/urandom");
         let reader_rng = ReaderRng::new(reader);
 
         OSRng { inner: reader_rng }
diff --git a/src/libstd/rand/reader.rs b/src/libstd/rand/reader.rs
index e19fbd9aaf8..621d70970f0 100644
--- a/src/libstd/rand/reader.rs
+++ b/src/libstd/rand/reader.rs
@@ -11,7 +11,7 @@
 //! A wrapper around any Reader to treat it as an RNG.
 
 use container::Container;
-use option::{Some, None};
+use result::{Ok, Err};
 use io::Reader;
 
 use rand::Rng;
@@ -49,26 +49,26 @@ impl<R: Reader> Rng for ReaderRng<R> {
         // platform just involves blitting the bytes into the memory
         // of the u32, similarly for BE on BE; avoiding byteswapping.
         if cfg!(target_endian="little") {
-            self.reader.read_le_u32()
+            self.reader.read_le_u32().unwrap()
         } else {
-            self.reader.read_be_u32()
+            self.reader.read_be_u32().unwrap()
         }
     }
     fn next_u64(&mut self) -> u64 {
         // see above for explanation.
         if cfg!(target_endian="little") {
-            self.reader.read_le_u64()
+            self.reader.read_le_u64().unwrap()
         } else {
-            self.reader.read_be_u64()
+            self.reader.read_be_u64().unwrap()
         }
     }
     fn fill_bytes(&mut self, v: &mut [u8]) {
         if v.len() == 0 { return }
         match self.reader.read(v) {
-            Some(n) if n == v.len() => return,
-            Some(n) => fail!("ReaderRng.fill_bytes could not fill buffer: \
-                              read {} out of {} bytes.", n, v.len()),
-            None => fail!("ReaderRng.fill_bytes reached eof.")
+            Ok(n) if n == v.len() => return,
+            Ok(n) => fail!("ReaderRng.fill_bytes could not fill buffer: \
+                            read {} out of {} bytes.", n, v.len()),
+            Err(e) => fail!("ReaderRng.fill_bytes error: {}", e)
         }
     }
 }
diff --git a/src/libstd/reflect.rs b/src/libstd/reflect.rs
index d6b4d3f5656..44ee5de7ac3 100644
--- a/src/libstd/reflect.rs
+++ b/src/libstd/reflect.rs
@@ -66,6 +66,8 @@ impl<V:TyVisitor + MovePtr> MovePtrAdaptor<V> {
     pub fn bump_past<T>(&mut self) {
         self.bump(mem::size_of::<T>());
     }
+
+    pub fn unwrap(self) -> V { self.inner }
 }
 
 /// Abstract type-directed pointer-movement using the MovePtr trait
diff --git a/src/libstd/repr.rs b/src/libstd/repr.rs
index 41ddf027787..f71649602b2 100644
--- a/src/libstd/repr.rs
+++ b/src/libstd/repr.rs
@@ -21,48 +21,57 @@ use char;
 use container::Container;
 use io;
 use iter::Iterator;
-use option::{Some, None};
+use option::{Some, None, Option};
 use ptr;
 use reflect;
 use reflect::{MovePtr, align};
+use result::{Ok, Err};
 use str::StrSlice;
 use to_str::ToStr;
 use vec::OwnedVector;
 use unstable::intrinsics::{Disr, Opaque, TyDesc, TyVisitor, get_tydesc, visit_tydesc};
 use unstable::raw;
 
+macro_rules! if_ok( ($me:expr, $e:expr) => (
+    match $e {
+        Ok(()) => {},
+        Err(e) => { $me.last_err = Some(e); return false; }
+    }
+) )
+
 /// Representations
 
 trait Repr {
-    fn write_repr(&self, writer: &mut io::Writer);
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()>;
 }
 
 impl Repr for () {
-    fn write_repr(&self, writer: &mut io::Writer) {
-        writer.write("()".as_bytes());
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
+        writer.write("()".as_bytes())
     }
 }
 
 impl Repr for bool {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         let s = if *self { "true" } else { "false" };
         writer.write(s.as_bytes())
     }
 }
 
 impl Repr for int {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         ::int::to_str_bytes(*self, 10u, |bits| {
-            writer.write(bits);
+            writer.write(bits)
         })
     }
 }
 
 macro_rules! int_repr(($ty:ident, $suffix:expr) => (impl Repr for $ty {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         ::$ty::to_str_bytes(*self, 10u, |bits| {
-            writer.write(bits);
-            writer.write(bytes!($suffix));
+            writer.write(bits).and_then(|()| {
+                writer.write(bytes!($suffix))
+            })
         })
     }
 }))
@@ -78,10 +87,11 @@ int_repr!(u32, "u32")
 int_repr!(u64, "u64")
 
 macro_rules! num_repr(($ty:ident, $suffix:expr) => (impl Repr for $ty {
-    fn write_repr(&self, writer: &mut io::Writer) {
+    fn write_repr(&self, writer: &mut io::Writer) -> io::IoResult<()> {
         let s = self.to_str();
-        writer.write(s.as_bytes());
-        writer.write(bytes!($suffix));
+        writer.write(s.as_bytes()).and_then(|()| {
+            writer.write(bytes!($suffix))
+        })
     }
 }))
 
@@ -100,7 +110,8 @@ pub struct ReprVisitor<'a> {
     priv ptr: *u8,
     priv ptr_stk: ~[*u8],
     priv var_stk: ~[VariantState],
-    priv writer: &'a mut io::Writer
+    priv writer: &'a mut io::Writer,
+    priv last_err: Option<io::IoError>,
 }
 
 pub fn ReprVisitor<'a>(ptr: *u8,
@@ -110,6 +121,7 @@ pub fn ReprVisitor<'a>(ptr: *u8,
         ptr_stk: ~[],
         var_stk: ~[],
         writer: writer,
+        last_err: None,
     }
 }
 
@@ -130,11 +142,10 @@ impl<'a> ReprVisitor<'a> {
     // Various helpers for the TyVisitor impl
 
     #[inline]
-    pub fn get<T>(&mut self, f: |&mut ReprVisitor, &T|) -> bool {
+    pub fn get<T>(&mut self, f: |&mut ReprVisitor, &T| -> bool) -> bool {
         unsafe {
-            f(self, transmute::<*u8,&T>(self.ptr));
+            f(self, transmute::<*u8,&T>(self.ptr))
         }
-        true
     }
 
     #[inline]
@@ -152,43 +163,53 @@ impl<'a> ReprVisitor<'a> {
                 ptr_stk: ~[],
                 var_stk: ~[],
                 writer: ::cast::transmute_copy(&self.writer),
+                last_err: None,
             };
             let mut v = reflect::MovePtrAdaptor(u);
             // Obviously this should not be a thing, but blame #8401 for now
             visit_tydesc(inner, &mut v as &mut TyVisitor);
-            true
+            match v.unwrap().last_err {
+                Some(e) => {
+                    self.last_err = Some(e);
+                    false
+                }
+                None => true,
+            }
         }
     }
 
     #[inline]
     pub fn write<T:Repr>(&mut self) -> bool {
         self.get(|this, v:&T| {
-            v.write_repr(unsafe { ::cast::transmute_copy(&this.writer) });
+            if_ok!(this, v.write_repr(this.writer));
+            true
         })
     }
 
-    pub fn write_escaped_slice(&mut self, slice: &str) {
-        self.writer.write(['"' as u8]);
+    pub fn write_escaped_slice(&mut self, slice: &str) -> bool {
+        if_ok!(self, self.writer.write(['"' as u8]));
         for ch in slice.chars() {
-            self.write_escaped_char(ch, true);
+            if !self.write_escaped_char(ch, true) { return false }
         }
-        self.writer.write(['"' as u8]);
+        if_ok!(self, self.writer.write(['"' as u8]));
+        true
     }
 
-    pub fn write_mut_qualifier(&mut self, mtbl: uint) {
+    pub fn write_mut_qualifier(&mut self, mtbl: uint) -> bool {
         if mtbl == 0 {
-            self.writer.write("mut ".as_bytes());
+            if_ok!(self, self.writer.write("mut ".as_bytes()));
         } else if mtbl == 1 {
             // skip, this is ast::m_imm
         } else {
             fail!("invalid mutability value");
         }
+        true
     }
 
     pub fn write_vec_range(&mut self, ptr: *(), len: uint, inner: *TyDesc) -> bool {
         let mut p = ptr as *u8;
         let (sz, al) = unsafe { ((*inner).size, (*inner).align) };
-        self.writer.write(['[' as u8]);
+        if_ok!(self, self.writer.write(['[' as u8]));
         let mut first = true;
         let mut left = len;
         // unit structs have 0 size, and don't loop forever.
@@ -197,13 +218,13 @@ impl<'a> ReprVisitor<'a> {
             if first {
                 first = false;
             } else {
-                self.writer.write(", ".as_bytes());
+                if_ok!(self, self.writer.write(", ".as_bytes()));
             }
             self.visit_ptr_inner(p as *u8, inner);
             p = align(unsafe { ptr::offset(p, sz as int) as uint }, al) as *u8;
             left -= dec;
         }
-        self.writer.write([']' as u8]);
+        if_ok!(self, self.writer.write([']' as u8]));
         true
     }
 
@@ -211,8 +232,8 @@ impl<'a> ReprVisitor<'a> {
         self.write_vec_range(ptr::to_unsafe_ptr(&v.data), v.fill, inner)
     }
 
-    fn write_escaped_char(&mut self, ch: char, is_str: bool) {
-        match ch {
+    fn write_escaped_char(&mut self, ch: char, is_str: bool) -> bool {
+        if_ok!(self, match ch {
             '\t' => self.writer.write("\\t".as_bytes()),
             '\r' => self.writer.write("\\r".as_bytes()),
             '\n' => self.writer.write("\\n".as_bytes()),
@@ -234,16 +255,18 @@ impl<'a> ReprVisitor<'a> {
             '\x20'..'\x7e' => self.writer.write([ch as u8]),
             _ => {
                 char::escape_unicode(ch, |c| {
-                    self.writer.write([c as u8]);
-                })
+                    let _ = self.writer.write([c as u8]);
+                });
+                Ok(())
             }
-        }
+        });
+        return true;
     }
 }
 
 impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_bot(&mut self) -> bool {
-        self.writer.write("!".as_bytes());
+        if_ok!(self, self.writer.write("!".as_bytes()));
         true
     }
     fn visit_nil(&mut self) -> bool { self.write::<()>() }
@@ -265,9 +288,10 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_char(&mut self) -> bool {
         self.get::<char>(|this, &ch| {
-            this.writer.write(['\'' as u8]);
-            this.write_escaped_char(ch, false);
-            this.writer.write(['\'' as u8]);
+            if_ok!(this, this.writer.write(['\'' as u8]));
+            if !this.write_escaped_char(ch, false) { return false }
+            if_ok!(this, this.writer.write(['\'' as u8]));
+            true
         })
     }
 
@@ -277,8 +301,8 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_estr_uniq(&mut self) -> bool {
         self.get::<~str>(|this, s| {
-            this.writer.write(['~' as u8]);
-            this.write_escaped_slice(*s);
+            if_ok!(this, this.writer.write(['~' as u8]));
+            this.write_escaped_slice(*s)
         })
     }
 
@@ -291,34 +315,35 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
                         _align: uint) -> bool { fail!(); }
 
     fn visit_box(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
-        self.writer.write(['@' as u8]);
+        if_ok!(self, self.writer.write(['@' as u8]));
         self.write_mut_qualifier(mtbl);
         self.get::<&raw::Box<()>>(|this, b| {
             let p = ptr::to_unsafe_ptr(&b.data) as *u8;
-            this.visit_ptr_inner(p, inner);
+            this.visit_ptr_inner(p, inner)
         })
     }
 
     fn visit_uniq(&mut self, _mtbl: uint, inner: *TyDesc) -> bool {
-        self.writer.write(['~' as u8]);
+        if_ok!(self, self.writer.write(['~' as u8]));
         self.get::<*u8>(|this, b| {
-            this.visit_ptr_inner(*b, inner);
+            this.visit_ptr_inner(*b, inner)
         })
     }
 
     fn visit_ptr(&mut self, mtbl: uint, _inner: *TyDesc) -> bool {
         self.get::<*u8>(|this, p| {
-            write!(this.writer, "({} as *", *p);
+            if_ok!(this, write!(this.writer, "({} as *", *p));
             this.write_mut_qualifier(mtbl);
-            this.writer.write("())".as_bytes());
+            if_ok!(this, this.writer.write("())".as_bytes()));
+            true
         })
     }
 
     fn visit_rptr(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
-        self.writer.write(['&' as u8]);
+        if_ok!(self, self.writer.write(['&' as u8]));
         self.write_mut_qualifier(mtbl);
         self.get::<*u8>(|this, p| {
-            this.visit_ptr_inner(*p, inner);
+            this.visit_ptr_inner(*p, inner)
         })
     }
 
@@ -327,33 +352,33 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_unboxed_vec(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<raw::Vec<()>>(|this, b| {
-            this.write_unboxed_vec_repr(mtbl, b, inner);
+            this.write_unboxed_vec_repr(mtbl, b, inner)
         })
     }
 
     fn visit_evec_box(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<&raw::Box<raw::Vec<()>>>(|this, b| {
-            this.writer.write(['@' as u8]);
+            if_ok!(this, this.writer.write(['@' as u8]));
             this.write_mut_qualifier(mtbl);
-            this.write_unboxed_vec_repr(mtbl, &b.data, inner);
+            this.write_unboxed_vec_repr(mtbl, &b.data, inner)
         })
     }
 
     fn visit_evec_uniq(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<&raw::Vec<()>>(|this, b| {
-            this.writer.write(['~' as u8]);
-            this.write_unboxed_vec_repr(mtbl, *b, inner);
+            if_ok!(this, this.writer.write(['~' as u8]));
+            this.write_unboxed_vec_repr(mtbl, *b, inner)
         })
     }
 
     fn visit_evec_slice(&mut self, mtbl: uint, inner: *TyDesc) -> bool {
         self.get::<raw::Slice<()>>(|this, s| {
-            this.writer.write(['&' as u8]);
+            if_ok!(this, this.writer.write(['&' as u8]));
             this.write_mut_qualifier(mtbl);
             let size = unsafe {
                 if (*inner).size == 0 { 1 } else { (*inner).size }
             };
-            this.write_vec_range(s.data, s.len * size, inner);
+            this.write_vec_range(s.data, s.len * size, inner)
         })
     }
 
@@ -361,42 +386,42 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
                         _: uint, inner: *TyDesc) -> bool {
         let assumed_size = if sz == 0 { n } else { sz };
         self.get::<()>(|this, b| {
-            this.write_vec_range(ptr::to_unsafe_ptr(b), assumed_size, inner);
+            this.write_vec_range(ptr::to_unsafe_ptr(b), assumed_size, inner)
         })
     }
 
     fn visit_enter_rec(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
-        self.writer.write(['{' as u8]);
+        if_ok!(self, self.writer.write(['{' as u8]));
         true
     }
 
     fn visit_rec_field(&mut self, i: uint, name: &str,
                        mtbl: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         self.write_mut_qualifier(mtbl);
-        self.writer.write(name.as_bytes());
-        self.writer.write(": ".as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
+        if_ok!(self, self.writer.write(": ".as_bytes()));
         self.visit_inner(inner);
         true
     }
 
     fn visit_leave_rec(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
-        self.writer.write(['}' as u8]);
+        if_ok!(self, self.writer.write(['}' as u8]));
         true
     }
 
     fn visit_enter_class(&mut self, name: &str, named_fields: bool, n_fields: uint,
                          _sz: uint, _align: uint) -> bool {
-        self.writer.write(name.as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
         if n_fields != 0 {
             if named_fields {
-                self.writer.write(['{' as u8]);
+                if_ok!(self, self.writer.write(['{' as u8]));
             } else {
-                self.writer.write(['(' as u8]);
+                if_ok!(self, self.writer.write(['(' as u8]));
             }
         }
         true
@@ -405,11 +430,11 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_class_field(&mut self, i: uint, name: &str, named: bool,
                          _mtbl: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         if named {
-            self.writer.write(name.as_bytes());
-            self.writer.write(": ".as_bytes());
+            if_ok!(self, self.writer.write(name.as_bytes()));
+            if_ok!(self, self.writer.write(": ".as_bytes()));
         }
         self.visit_inner(inner);
         true
@@ -419,9 +444,9 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
                          _sz: uint, _align: uint) -> bool {
         if n_fields != 0 {
             if named_fields {
-                self.writer.write(['}' as u8]);
+                if_ok!(self, self.writer.write(['}' as u8]));
             } else {
-                self.writer.write([')' as u8]);
+                if_ok!(self, self.writer.write([')' as u8]));
             }
         }
         true
@@ -429,13 +454,13 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_enter_tup(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
-        self.writer.write(['(' as u8]);
+        if_ok!(self, self.writer.write(['(' as u8]));
         true
     }
 
     fn visit_tup_field(&mut self, i: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         self.visit_inner(inner);
         true
@@ -444,9 +469,9 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_leave_tup(&mut self, _n_fields: uint,
                        _sz: uint, _align: uint) -> bool {
         if _n_fields == 1 {
-            self.writer.write([',' as u8]);
+            if_ok!(self, self.writer.write([',' as u8]));
         }
-        self.writer.write([')' as u8]);
+        if_ok!(self, self.writer.write([')' as u8]));
         true
     }
 
@@ -482,9 +507,9 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
         }
 
         if write {
-            self.writer.write(name.as_bytes());
+            if_ok!(self, self.writer.write(name.as_bytes()));
             if n_fields > 0 {
-                self.writer.write(['(' as u8]);
+                if_ok!(self, self.writer.write(['(' as u8]));
             }
         }
         true
@@ -498,7 +523,7 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
         match self.var_stk[self.var_stk.len() - 1] {
             Matched => {
                 if i != 0 {
-                    self.writer.write(", ".as_bytes());
+                    if_ok!(self, self.writer.write(", ".as_bytes()));
                 }
                 if ! self.visit_inner(inner) {
                     return false;
@@ -516,7 +541,7 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
         match self.var_stk[self.var_stk.len() - 1] {
             Matched => {
                 if n_fields > 0 {
-                    self.writer.write([')' as u8]);
+                    if_ok!(self, self.writer.write([')' as u8]));
                 }
             }
             _ => ()
@@ -538,28 +563,29 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
     fn visit_enter_fn(&mut self, _purity: uint, _proto: uint,
                       _n_inputs: uint, _retstyle: uint) -> bool {
-        self.writer.write("fn(".as_bytes());
+        if_ok!(self, self.writer.write("fn(".as_bytes()));
         true
     }
 
     fn visit_fn_input(&mut self, i: uint, _mode: uint, inner: *TyDesc) -> bool {
         if i != 0 {
-            self.writer.write(", ".as_bytes());
+            if_ok!(self, self.writer.write(", ".as_bytes()));
         }
         let name = unsafe { (*inner).name };
-        self.writer.write(name.as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
         true
     }
 
-    fn visit_fn_output(&mut self, _retstyle: uint, variadic: bool, inner: *TyDesc) -> bool {
+    fn visit_fn_output(&mut self, _retstyle: uint, variadic: bool,
+                       inner: *TyDesc) -> bool {
         if variadic {
-            self.writer.write(", ...".as_bytes());
+            if_ok!(self, self.writer.write(", ...".as_bytes()));
         }
-        self.writer.write(")".as_bytes());
+        if_ok!(self, self.writer.write(")".as_bytes()));
         let name = unsafe { (*inner).name };
         if name != "()" {
-            self.writer.write(" -> ".as_bytes());
-            self.writer.write(name.as_bytes());
+            if_ok!(self, self.writer.write(" -> ".as_bytes()));
+            if_ok!(self, self.writer.write(name.as_bytes()));
         }
         true
     }
@@ -569,7 +595,7 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
 
 
     fn visit_trait(&mut self, name: &str) -> bool {
-        self.writer.write(name.as_bytes());
+        if_ok!(self, self.writer.write(name.as_bytes()));
         true
     }
 
@@ -582,13 +608,17 @@ impl<'a> TyVisitor for ReprVisitor<'a> {
     fn visit_closure_ptr(&mut self, _ck: uint) -> bool { true }
 }
 
-pub fn write_repr<T>(writer: &mut io::Writer, object: &T) {
+pub fn write_repr<T>(writer: &mut io::Writer, object: &T) -> io::IoResult<()> {
     unsafe {
         let ptr = ptr::to_unsafe_ptr(object) as *u8;
         let tydesc = get_tydesc::<T>();
         let u = ReprVisitor(ptr, writer);
         let mut v = reflect::MovePtrAdaptor(u);
         visit_tydesc(tydesc, &mut v as &mut TyVisitor);
+        match v.unwrap().last_err {
+            Some(e) => Err(e),
+            None => Ok(()),
+        }
     }
 }
 
@@ -597,7 +627,7 @@ pub fn repr_to_str<T>(t: &T) -> ~str {
     use io;
 
     let mut result = io::MemWriter::new();
-    write_repr(&mut result as &mut io::Writer, t);
+    write_repr(&mut result as &mut io::Writer, t).unwrap();
     str::from_utf8_owned(result.unwrap()).unwrap()
 }
 
@@ -615,7 +645,7 @@ fn test_repr() {
 
     fn exact_test<T>(t: &T, e:&str) {
         let mut m = io::MemWriter::new();
-        write_repr(&mut m as &mut io::Writer, t);
+        write_repr(&mut m as &mut io::Writer, t).unwrap();
         let s = str::from_utf8_owned(m.unwrap()).unwrap();
         assert_eq!(s.as_slice(), e);
     }
diff --git a/src/libstd/result.rs b/src/libstd/result.rs
index cc8fdeaccfe..846bba7533f 100644
--- a/src/libstd/result.rs
+++ b/src/libstd/result.rs
@@ -208,7 +208,7 @@ impl<T, E> Result<T, E> {
 
 impl<T: fmt::Show, E: fmt::Show> fmt::Show for Result<T, E> {
     #[inline]
-    fn fmt(s: &Result<T, E>, f: &mut fmt::Formatter) {
+    fn fmt(s: &Result<T, E>, f: &mut fmt::Formatter) -> fmt::Result {
         match *s {
             Ok(ref t) => write!(f.buf, "Ok({})", *t),
             Err(ref e) => write!(f.buf, "Err({})", *e)
diff --git a/src/libstd/rt/rtio.rs b/src/libstd/rt/rtio.rs
index 455a84b4ce3..35b1e21df06 100644
--- a/src/libstd/rt/rtio.rs
+++ b/src/libstd/rt/rtio.rs
@@ -16,13 +16,13 @@ use libc;
 use ops::Drop;
 use option::{Option, Some, None};
 use path::Path;
-use result::{Result, Ok, Err};
+use result::{Result, Err};
 use rt::task::Task;
 use rt::local::Local;
 
 use ai = io::net::addrinfo;
 use io;
-use io::IoError;
+use io::{IoError, IoResult};
 use io::net::ip::{IpAddr, SocketAddr};
 use io::process::{ProcessConfig, ProcessExit};
 use io::signal::Signum;
@@ -116,23 +116,12 @@ impl<'a> LocalIo<'a> {
         return ret;
     }
 
-    pub fn maybe_raise<T>(f: |io: &mut IoFactory| -> Result<T, IoError>)
-        -> Option<T>
+    pub fn maybe_raise<T>(f: |io: &mut IoFactory| -> IoResult<T>)
+        -> IoResult<T>
     {
         match LocalIo::borrow() {
-            None => {
-                io::io_error::cond.raise(io::standard_error(io::IoUnavailable));
-                None
-            }
-            Some(mut io) => {
-                match f(io.get()) {
-                    Ok(t) => Some(t),
-                    Err(ioerr) => {
-                        io::io_error::cond.raise(ioerr);
-                        None
-                    }
-                }
-            }
+            None => Err(io::standard_error(io::IoUnavailable)),
+            Some(mut io) => f(io.get()),
         }
     }
 
diff --git a/src/libstd/rt/task.rs b/src/libstd/rt/task.rs
index 7c43e64f17b..515eb93001a 100644
--- a/src/libstd/rt/task.rs
+++ b/src/libstd/rt/task.rs
@@ -119,6 +119,7 @@ impl Task {
 
             // Run the task main function, then do some cleanup.
             f.finally(|| {
+                #[allow(unused_must_use)]
                 fn close_outputs() {
                     let mut task = Local::borrow(None::<Task>);
                     let logger = task.get().logger.take();
@@ -126,8 +127,8 @@ impl Task {
                     let stdout = task.get().stdout.take();
                     drop(task);
                     drop(logger); // loggers are responsible for flushing
-                    match stdout { Some(mut w) => w.flush(), None => {} }
-                    match stderr { Some(mut w) => w.flush(), None => {} }
+                    match stdout { Some(mut w) => { w.flush(); }, None => {} }
+                    match stderr { Some(mut w) => { w.flush(); }, None => {} }
                 }
 
                 // First, flush/destroy the user stdout/logger because these
diff --git a/src/libstd/rt/unwind.rs b/src/libstd/rt/unwind.rs
index 4d2dcb6c51c..9aece13b84c 100644
--- a/src/libstd/rt/unwind.rs
+++ b/src/libstd/rt/unwind.rs
@@ -464,9 +464,10 @@ fn begin_unwind_inner(msg: ~Any, file: &'static str, line: uint) -> ! {
             match task.stderr.take() {
                 Some(mut stderr) => {
                     Local::put(task);
-                    format_args!(|args| ::fmt::writeln(stderr, args),
-                                 "task '{}' failed at '{}', {}:{}",
-                                 n, msg_s, file, line);
+                    // FIXME: what to do when the task printing fails?
+                    let _err = format_args!(|args| ::fmt::writeln(stderr, args),
+                                            "task '{}' failed at '{}', {}:{}",
+                                            n, msg_s, file, line);
                     task = Local::take();
 
                     match util::replace(&mut task.stderr, Some(stderr)) {
diff --git a/src/libstd/rt/util.rs b/src/libstd/rt/util.rs
index 9c17c624987..69e240f30bc 100644
--- a/src/libstd/rt/util.rs
+++ b/src/libstd/rt/util.rs
@@ -11,10 +11,12 @@
 use container::Container;
 use fmt;
 use from_str::FromStr;
+use io::IoResult;
 use iter::Iterator;
 use libc;
 use option::{Some, None, Option};
 use os;
+use result::Ok;
 use str::StrSlice;
 use unstable::running_on_valgrind;
 use vec::ImmutableVector;
@@ -73,16 +75,17 @@ pub fn dumb_println(args: &fmt::Arguments) {
 
     struct Stderr;
     impl io::Writer for Stderr {
-        fn write(&mut self, data: &[u8]) {
+        fn write(&mut self, data: &[u8]) -> IoResult<()> {
             unsafe {
                 libc::write(libc::STDERR_FILENO,
                             data.as_ptr() as *libc::c_void,
                             data.len() as libc::size_t);
             }
+            Ok(()) // yes, we're lying
         }
     }
     let mut w = Stderr;
-    fmt::writeln(&mut w as &mut io::Writer, args);
+    let _ = fmt::writeln(&mut w as &mut io::Writer, args);
 }
 
 pub fn abort(msg: &str) -> ! {
diff --git a/src/libstd/run.rs b/src/libstd/run.rs
index ef2374f6095..04e42b3eedf 100644
--- a/src/libstd/run.rs
+++ b/src/libstd/run.rs
@@ -11,6 +11,7 @@
 //! Utilities for spawning and managing processes
 
 #[allow(missing_doc)];
+#[deny(unused_must_use)];
 
 use comm::SharedChan;
 use io::Reader;
@@ -119,7 +120,8 @@ impl Process {
      * * options - Options to configure the environment of the process,
      *             the working directory and the standard IO streams.
      */
-    pub fn new(prog: &str, args: &[~str], options: ProcessOptions) -> Option<Process> {
+    pub fn new(prog: &str, args: &[~str],
+               options: ProcessOptions) -> io::IoResult<Process> {
         let ProcessOptions { env, dir, in_fd, out_fd, err_fd } = options;
         let env = env.as_ref().map(|a| a.as_slice());
         let cwd = dir.as_ref().map(|a| a.as_str().unwrap());
@@ -138,10 +140,7 @@ impl Process {
             cwd: cwd,
             io: rtio,
         };
-        match process::Process::new(rtconfig) {
-            Some(inner) => Some(Process { inner: inner }),
-            None => None
-        }
+        process::Process::new(rtconfig).map(|p| Process { inner: p })
     }
 
     /// Returns the unique id of the process
@@ -224,19 +223,17 @@ impl Process {
         let ch_clone = ch.clone();
 
         spawn(proc() {
-            let _guard = io::ignore_io_error();
             let mut error = error;
             match error {
                 Some(ref mut e) => ch.send((2, e.read_to_end())),
-                None => ch.send((2, ~[]))
+                None => ch.send((2, Ok(~[])))
             }
         });
         spawn(proc() {
-            let _guard = io::ignore_io_error();
             let mut output = output;
             match output {
                 Some(ref mut e) => ch_clone.send((1, e.read_to_end())),
-                None => ch_clone.send((1, ~[]))
+                None => ch_clone.send((1, Ok(~[])))
             }
         });
 
@@ -251,8 +248,8 @@ impl Process {
         };
 
         return ProcessOutput {status: status,
-                              output: outs,
-                              error: errs};
+                              output: outs.ok().unwrap_or(~[]),
+                              error: errs.ok().unwrap_or(~[]) };
     }
 
     /**
@@ -262,9 +259,10 @@ impl Process {
      * On Posix OSs SIGTERM will be sent to the process. On Win32
      * TerminateProcess(..) will be called.
      */
-    pub fn destroy(&mut self) {
-        self.inner.signal(io::process::PleaseExitSignal);
+    pub fn destroy(&mut self) -> io::IoResult<()> {
+        let ret = self.inner.signal(io::process::PleaseExitSignal);
         self.finish();
+        return ret;
     }
 
     /**
@@ -274,9 +272,12 @@ impl Process {
      * On Posix OSs SIGKILL will be sent to the process. On Win32
      * TerminateProcess(..) will be called.
      */
-    pub fn force_destroy(&mut self) {
-        self.inner.signal(io::process::MustDieSignal);
+    pub fn force_destroy(&mut self) -> io::IoResult<()> {
+        // This should never fail because we own the process
+        let ret = self.inner.signal(io::process::MustDieSignal);
         self.finish();
+        return ret;
+
     }
 }
 
@@ -293,18 +294,14 @@ impl Process {
  *
  * The process's exit code, or None if the child process could not be started
  */
-pub fn process_status(prog: &str, args: &[~str]) -> Option<ProcessExit> {
-    let mut opt_prog = Process::new(prog, args, ProcessOptions {
+pub fn process_status(prog: &str, args: &[~str]) -> io::IoResult<ProcessExit> {
+    Process::new(prog, args, ProcessOptions {
         env: None,
         dir: None,
         in_fd: Some(unsafe { libc::dup(libc::STDIN_FILENO) }),
         out_fd: Some(unsafe { libc::dup(libc::STDOUT_FILENO) }),
         err_fd: Some(unsafe { libc::dup(libc::STDERR_FILENO) })
-    });
-    match opt_prog {
-        Some(ref mut prog) => Some(prog.finish()),
-        None => None
-    }
+    }).map(|mut p| p.finish())
 }
 
 /**
@@ -320,12 +317,10 @@ pub fn process_status(prog: &str, args: &[~str]) -> Option<ProcessExit> {
  * The process's stdout/stderr output and exit code, or None if the child process could not be
  * started.
  */
-pub fn process_output(prog: &str, args: &[~str]) -> Option<ProcessOutput> {
-    let mut opt_prog = Process::new(prog, args, ProcessOptions::new());
-    match opt_prog {
-        Some(ref mut prog) => Some(prog.finish_with_output()),
-        None => None
-    }
+pub fn process_output(prog: &str, args: &[~str]) -> io::IoResult<ProcessOutput> {
+    Process::new(prog, args, ProcessOptions::new()).map(|mut p| {
+        p.finish_with_output()
+    })
 }
 
 #[cfg(test)]
@@ -337,33 +332,25 @@ mod tests {
     use task::spawn;
     use unstable::running_on_valgrind;
     use io::pipe::PipeStream;
-    use io::{io_error, FileNotFound};
+    use io::{FileNotFound};
     use libc::c_int;
 
     #[test]
     #[cfg(not(target_os="android"))] // FIXME(#10380)
     fn test_process_status() {
-        let mut status = run::process_status("false", []).expect("failed to exec `false`");
+        let mut status = run::process_status("false", []).unwrap();
         assert!(status.matches_exit_status(1));
 
-        status = run::process_status("true", []).expect("failed to exec `true`");
+        status = run::process_status("true", []).unwrap();
         assert!(status.success());
     }
 
     #[test]
     fn test_process_output_fail_to_start() {
-        // If the executable does not exist, then the io_error condition should be raised with
-        // IoErrorKind FileNotFound.
-
-        let mut trapped_io_error = false;
-        let opt_outp = io_error::cond.trap(|e| {
-            trapped_io_error = true;
-            assert_eq!(e.kind, FileNotFound);
-        }).inside(|| -> Option<run::ProcessOutput> {
-            run::process_output("/no-binary-by-this-name-should-exist", [])
-        });
-        assert!(trapped_io_error);
-        assert!(opt_outp.is_none());
+        match run::process_output("/no-binary-by-this-name-should-exist", []) {
+            Err(e) => assert_eq!(e.kind, FileNotFound),
+            Ok(..) => fail!()
+        }
     }
 
     #[test]
@@ -371,7 +358,7 @@ mod tests {
     fn test_process_output_output() {
 
         let run::ProcessOutput {status, output, error}
-             = run::process_output("echo", [~"hello"]).expect("failed to exec `echo`");
+             = run::process_output("echo", [~"hello"]).unwrap();
         let output_str = str::from_utf8_owned(output).unwrap();
 
         assert!(status.success());
@@ -387,7 +374,7 @@ mod tests {
     fn test_process_output_error() {
 
         let run::ProcessOutput {status, output, error}
-             = run::process_output("mkdir", [~"."]).expect("failed to exec `mkdir`");
+             = run::process_output("mkdir", [~"."]).unwrap();
 
         assert!(status.matches_exit_status(1));
         assert_eq!(output, ~[]);
@@ -408,7 +395,7 @@ mod tests {
             in_fd: Some(pipe_in.input),
             out_fd: Some(pipe_out.out),
             err_fd: Some(pipe_err.out)
-        }).expect("failed to exec `cat`");
+        }).unwrap();
 
         os::close(pipe_in.input as int);
         os::close(pipe_out.out as int);
@@ -426,27 +413,18 @@ mod tests {
 
     fn writeclose(fd: c_int, s: &str) {
         let mut writer = PipeStream::open(fd);
-        writer.write(s.as_bytes());
+        writer.write(s.as_bytes()).unwrap();
     }
 
     fn readclose(fd: c_int) -> ~str {
-        let mut res = ~[];
-        let mut reader = PipeStream::open(fd);
-        let mut buf = [0, ..1024];
-        loop {
-            match reader.read(buf) {
-                Some(n) => { res.push_all(buf.slice_to(n)); }
-                None => break
-            }
-        }
-        str::from_utf8_owned(res).unwrap()
+        PipeStream::open(fd).read_to_str().unwrap()
     }
 
     #[test]
     #[cfg(not(target_os="android"))] // FIXME(#10380)
     fn test_finish_once() {
         let mut prog = run::Process::new("false", [], run::ProcessOptions::new())
-            .expect("failed to exec `false`");
+            .unwrap();
         assert!(prog.finish().matches_exit_status(1));
     }
 
@@ -454,7 +432,7 @@ mod tests {
     #[cfg(not(target_os="android"))] // FIXME(#10380)
     fn test_finish_twice() {
         let mut prog = run::Process::new("false", [], run::ProcessOptions::new())
-            .expect("failed to exec `false`");
+            .unwrap();
         assert!(prog.finish().matches_exit_status(1));
         assert!(prog.finish().matches_exit_status(1));
     }
@@ -464,7 +442,7 @@ mod tests {
     fn test_finish_with_output_once() {
 
         let mut prog = run::Process::new("echo", [~"hello"], run::ProcessOptions::new())
-            .expect("failed to exec `echo`");
+            .unwrap();
         let run::ProcessOutput {status, output, error}
             = prog.finish_with_output();
         let output_str = str::from_utf8_owned(output).unwrap();
@@ -482,7 +460,7 @@ mod tests {
     fn test_finish_with_output_twice() {
 
         let mut prog = run::Process::new("echo", [~"hello"], run::ProcessOptions::new())
-            .expect("failed to exec `echo`");
+            .unwrap();
         let run::ProcessOutput {status, output, error}
             = prog.finish_with_output();
 
@@ -511,14 +489,14 @@ mod tests {
         run::Process::new("pwd", [], run::ProcessOptions {
             dir: dir,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `pwd`")
+        }).unwrap()
     }
     #[cfg(unix,target_os="android")]
     fn run_pwd(dir: Option<&Path>) -> run::Process {
         run::Process::new("/system/bin/sh", [~"-c",~"pwd"], run::ProcessOptions {
             dir: dir,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `/system/bin/sh`")
+        }).unwrap()
     }
 
     #[cfg(windows)]
@@ -526,7 +504,7 @@ mod tests {
         run::Process::new("cmd", [~"/c", ~"cd"], run::ProcessOptions {
             dir: dir,
             .. run::ProcessOptions::new()
-        }).expect("failed to run `cmd`")
+        }).unwrap()
     }
 
     #[test]
@@ -537,8 +515,8 @@ mod tests {
         let parent_dir = os::getcwd();
         let child_dir = Path::new(output.trim());
 
-        let parent_stat = parent_dir.stat();
-        let child_stat = child_dir.stat();
+        let parent_stat = parent_dir.stat().unwrap();
+        let child_stat = child_dir.stat().unwrap();
 
         assert_eq!(parent_stat.unstable.device, child_stat.unstable.device);
         assert_eq!(parent_stat.unstable.inode, child_stat.unstable.inode);
@@ -554,8 +532,8 @@ mod tests {
         let output = str::from_utf8_owned(prog.finish_with_output().output).unwrap();
         let child_dir = Path::new(output.trim());
 
-        let parent_stat = parent_dir.stat();
-        let child_stat = child_dir.stat();
+        let parent_stat = parent_dir.stat().unwrap();
+        let child_stat = child_dir.stat().unwrap();
 
         assert_eq!(parent_stat.unstable.device, child_stat.unstable.device);
         assert_eq!(parent_stat.unstable.inode, child_stat.unstable.inode);
@@ -566,14 +544,14 @@ mod tests {
         run::Process::new("env", [], run::ProcessOptions {
             env: env,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `env`")
+        }).unwrap()
     }
     #[cfg(unix,target_os="android")]
     fn run_env(env: Option<~[(~str, ~str)]>) -> run::Process {
         run::Process::new("/system/bin/sh", [~"-c",~"set"], run::ProcessOptions {
             env: env,
             .. run::ProcessOptions::new()
-        }).expect("failed to exec `/system/bin/sh`")
+        }).unwrap()
     }
 
     #[cfg(windows)]
@@ -581,7 +559,7 @@ mod tests {
         run::Process::new("cmd", [~"/c", ~"set"], run::ProcessOptions {
             env: env,
             .. run::ProcessOptions::new()
-        }).expect("failed to run `cmd`")
+        }).unwrap()
     }
 
     #[test]
diff --git a/src/libstd/task.rs b/src/libstd/task.rs
index c8b69083086..5fa0c6431ab 100644
--- a/src/libstd/task.rs
+++ b/src/libstd/task.rs
@@ -541,7 +541,7 @@ fn test_avoid_copying_the_body_task_spawn() {
 #[test]
 fn test_avoid_copying_the_body_try() {
     avoid_copying_the_body(|f| {
-        try(proc() {
+        let _ = try(proc() {
             f()
         });
     })
diff --git a/src/libstd/to_bytes.rs b/src/libstd/to_bytes.rs
index 4c545de73b4..c8bd1907c5c 100644
--- a/src/libstd/to_bytes.rs
+++ b/src/libstd/to_bytes.rs
@@ -349,7 +349,7 @@ impl<A:IterBytes> ToBytes for A {
 
         let mut m = ::io::MemWriter::new();
         self.iter_bytes(lsb0, |bytes| {
-            m.write(bytes);
+            m.write(bytes).unwrap();
             true
         });
         m.unwrap()
diff --git a/src/libstd/unstable/sync.rs b/src/libstd/unstable/sync.rs
index 3b2c86c3712..c2fa168a478 100644
--- a/src/libstd/unstable/sync.rs
+++ b/src/libstd/unstable/sync.rs
@@ -200,7 +200,7 @@ mod tests {
             // accesses will also fail.
             let x = Exclusive::new(1);
             let x2 = x.clone();
-            task::try(proc() {
+            let _ = task::try(proc() {
                 x2.with(|one| assert_eq!(*one, 2))
             });
             x.with(|one| assert_eq!(*one, 1));