| // 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. |
| |
| #![allow(non_camel_case_types)] |
| |
| |
| |
| 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()]); |
| } |