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// Copyright 2012-2014 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.
trait vec_monad<A> {
fn bind<B, F>(&self, f: F ) -> Vec<B> where F: FnMut(&A) -> Vec<B> ;
}
impl<A> vec_monad<A> for Vec<A> {
fn bind<B, F>(&self, mut f: F) -> Vec<B> where F: FnMut(&A) -> Vec<B> {
let mut r = Vec::new();
for elt in self {
r.extend(f(elt));
}
r
}
}
trait option_monad<A> {
fn bind<B, F>(&self, f: F) -> Option<B> where F: FnOnce(&A) -> Option<B>;
}
impl<A> option_monad<A> for Option<A> {
fn bind<B, F>(&self, f: F) -> Option<B> where F: FnOnce(&A) -> Option<B> {
match *self {
Some(ref a) => { f(a) }
None => { None }
}
}
}
fn transform(x: Option<isize>) -> Option<String> {
x.bind(|n| Some(*n + 1) ).bind(|n| Some(n.to_string()) )
}
pub fn main() {
assert_eq!(transform(Some(10)), Some("11".to_string()));
assert_eq!(transform(None), None);
assert_eq!((vec!("hi".to_string()))
.bind(|x| vec!(x.clone(), format!("{}!", x)) )
.bind(|x| vec!(x.clone(), format!("{}?", x)) ),
["hi".to_string(),
"hi?".to_string(),
"hi!".to_string(),
"hi!?".to_string()]);
}
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