50 lines
1.3 KiB
Rust
50 lines
1.3 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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trait vec_monad<A> {
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fn bind<B:Copy>(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:Copy>(f: fn(&A) -> ~[B]) -> ~[B] {
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let mut r = ~[];
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for self.each |elt| { r += f(elt); }
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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: 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>(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(int::str(*n)) )
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}
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pub fn main() {
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assert transform(Some(10)) == Some(~"11");
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assert transform(None) == None;
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assert (~[~"hi"])
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.bind(|x| ~[copy *x, *x + ~"!"] )
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.bind(|x| ~[copy *x, *x + ~"?"] ) ==
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~[~"hi", ~"hi?", ~"hi!", ~"hi!?"];
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}
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