49 lines
1.2 KiB
Rust
49 lines
1.2 KiB
Rust
//@ run-pass
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#![allow(non_camel_case_types)]
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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));
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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<isize>) -> 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_eq!((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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["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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