54 lines
1.4 KiB
Rust
54 lines
1.4 KiB
Rust
// Copyright 2012 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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// xfail-fast
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use std::int;
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trait vec_monad<A> {
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fn bind<B>(&self, f: &fn(&A) -> ~[B]) -> ~[B];
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}
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impl<A> vec_monad<A> for ~[A] {
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fn bind<B>(&self, f: &fn(&A) -> ~[B]) -> ~[B] {
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let mut r = ~[];
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for elt in self.iter() {
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r.push_all_move(f(elt));
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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>(&self, f: &fn(&A) -> Option<B>) -> 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>(&self, f: &fn(&A) -> Option<B>) -> 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<~str> {
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x.bind(|n| Some(*n + 1) ).bind(|n| Some(n.to_str()) )
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}
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pub fn main() {
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assert_eq!(transform(Some(10)), Some(~"11"));
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assert_eq!(transform(None), None);
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assert!((~[~"hi"])
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.bind(|x| ~[x.clone(), *x + "!"] )
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.bind(|x| ~[x.clone(), *x + "?"] ) ==
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~[~"hi", ~"hi?", ~"hi!", ~"hi!?"]);
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}
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