55 lines
1.6 KiB
Rust
55 lines
1.6 KiB
Rust
// Copyright 2012-2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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trait vec_monad<A> {
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fn bind<B, F>(&self, f: F ) -> Vec<B> where F: FnMut(&A) -> Vec<B> ;
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}
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impl<A> vec_monad<A> for Vec<A> {
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fn bind<B, F>(&self, mut f: F) -> Vec<B> where F: FnMut(&A) -> Vec<B> {
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let mut r = Vec::new();
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for elt in self {
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r.extend(f(elt).into_iter());
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}
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r
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}
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}
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trait option_monad<A> {
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fn bind<B, F>(&self, f: F) -> Option<B> where F: FnOnce(&A) -> Option<B>;
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}
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impl<A> option_monad<A> for Option<A> {
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fn bind<B, F>(&self, f: F) -> Option<B> where F: FnOnce(&A) -> Option<B> {
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match *self {
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Some(ref a) => { f(a) }
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None => { None }
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}
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}
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}
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fn transform(x: Option<int>) -> Option<String> {
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x.bind(|n| Some(*n + 1) ).bind(|n| Some(n.to_string()) )
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}
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pub fn main() {
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assert_eq!(transform(Some(10)), Some("11".to_string()));
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assert_eq!(transform(None), None);
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assert!((vec!("hi".to_string()))
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.bind(|x| vec!(x.clone(), format!("{}!", x)) )
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.bind(|x| vec!(x.clone(), format!("{}?", x)) ) ==
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vec!("hi".to_string(),
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"hi?".to_string(),
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"hi!".to_string(),
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"hi!?".to_string()));
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}
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