28 lines
645 B
Rust
28 lines
645 B
Rust
impl monad<A> for ~[A] {
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fn bind<B>(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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impl monad<A> for option<A> {
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fn bind<B>(f: fn(A) -> option<B>) -> option<B> {
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alt self {
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some(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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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"]).bind(|x| ~[x, x + "!"] ).bind(|x| ~[x, x + "?"] ) ==
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~["hi", "hi?", "hi!", "hi!?"];
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}
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