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|
//! A type that represents one of two alternatives
import result::result;
/// The either type
enum either<T, U> {
left(T),
right(U)
}
fn either<T, U, V>(f_left: fn(T) -> V,
f_right: fn(U) -> V, value: either<T, U>) -> V {
/*!
* Applies a function based on the given either value
*
* If `value` is left(T) then `f_left` is applied to its contents, if
* `value` is right(U) then `f_right` is applied to its contents, and the
* result is returned.
*/
alt value { left(l) { f_left(l) } right(r) { f_right(r) } }
}
fn lefts<T: copy, U>(eithers: ~[either<T, U>]) -> ~[T] {
//! Extracts from a vector of either all the left values
let mut result: ~[T] = ~[];
for vec::each(eithers) |elt| {
alt elt { left(l) { vec::push(result, l); } _ {/* fallthrough */ } }
}
ret result;
}
fn rights<T, U: copy>(eithers: ~[either<T, U>]) -> ~[U] {
//! Extracts from a vector of either all the right values
let mut result: ~[U] = ~[];
for vec::each(eithers) |elt| {
alt elt { right(r) { vec::push(result, r); } _ {/* fallthrough */ } }
}
ret result;
}
fn partition<T: copy, U: copy>(eithers: ~[either<T, U>])
-> {lefts: ~[T], rights: ~[U]} {
/*!
* Extracts from a vector of either all the left values and right values
*
* Returns a structure containing a vector of left values and a vector of
* right values.
*/
let mut lefts: ~[T] = ~[];
let mut rights: ~[U] = ~[];
for vec::each(eithers) |elt| {
alt elt {
left(l) { vec::push(lefts, l); }
right(r) { vec::push(rights, r); }
}
}
ret {lefts: lefts, rights: rights};
}
pure fn flip<T: copy, U: copy>(eith: either<T, U>) -> either<U, T> {
//! Flips between left and right of a given either
alt eith {
right(r) { left(r) }
left(l) { right(l) }
}
}
pure fn to_result<T: copy, U: copy>(
eith: either<T, U>) -> result<U, T> {
/*!
* Converts either::t to a result::t
*
* Converts an `either` type to a `result` type, making the "right" choice
* an ok result, and the "left" choice a fail
*/
alt eith {
right(r) { result::ok(r) }
left(l) { result::err(l) }
}
}
pure fn is_left<T, U>(eith: either<T, U>) -> bool {
//! Checks whether the given value is a left
alt eith { left(_) { true } _ { false } }
}
pure fn is_right<T, U>(eith: either<T, U>) -> bool {
//! Checks whether the given value is a right
alt eith { right(_) { true } _ { false } }
}
#[test]
fn test_either_left() {
let val = left(10);
fn f_left(&&x: int) -> bool { x == 10 }
fn f_right(&&_x: uint) -> bool { false }
assert (either(f_left, f_right, val));
}
#[test]
fn test_either_right() {
let val = right(10u);
fn f_left(&&_x: int) -> bool { false }
fn f_right(&&x: uint) -> bool { x == 10u }
assert (either(f_left, f_right, val));
}
#[test]
fn test_lefts() {
let input = ~[left(10), right(11), left(12), right(13), left(14)];
let result = lefts(input);
assert (result == ~[10, 12, 14]);
}
#[test]
fn test_lefts_none() {
let input: ~[either<int, int>] = ~[right(10), right(10)];
let result = lefts(input);
assert (vec::len(result) == 0u);
}
#[test]
fn test_lefts_empty() {
let input: ~[either<int, int>] = ~[];
let result = lefts(input);
assert (vec::len(result) == 0u);
}
#[test]
fn test_rights() {
let input = ~[left(10), right(11), left(12), right(13), left(14)];
let result = rights(input);
assert (result == ~[11, 13]);
}
#[test]
fn test_rights_none() {
let input: ~[either<int, int>] = ~[left(10), left(10)];
let result = rights(input);
assert (vec::len(result) == 0u);
}
#[test]
fn test_rights_empty() {
let input: ~[either<int, int>] = ~[];
let result = rights(input);
assert (vec::len(result) == 0u);
}
#[test]
fn test_partition() {
let input = ~[left(10), right(11), left(12), right(13), left(14)];
let result = partition(input);
assert (result.lefts[0] == 10);
assert (result.lefts[1] == 12);
assert (result.lefts[2] == 14);
assert (result.rights[0] == 11);
assert (result.rights[1] == 13);
}
#[test]
fn test_partition_no_lefts() {
let input: ~[either<int, int>] = ~[right(10), right(11)];
let result = partition(input);
assert (vec::len(result.lefts) == 0u);
assert (vec::len(result.rights) == 2u);
}
#[test]
fn test_partition_no_rights() {
let input: ~[either<int, int>] = ~[left(10), left(11)];
let result = partition(input);
assert (vec::len(result.lefts) == 2u);
assert (vec::len(result.rights) == 0u);
}
#[test]
fn test_partition_empty() {
let input: ~[either<int, int>] = ~[];
let result = partition(input);
assert (vec::len(result.lefts) == 0u);
assert (vec::len(result.rights) == 0u);
}
//
// Local Variables:
// mode: rust
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// End:
//
|
