trait Monad<T> {
	fn ret(T) -> self;
	fn bind<U>(fn(&T) -> Monad<U>) -> Monad<U>;
}

impl<T> Option<T>: Monad<T> {
	fn ret(value: T) -> Option<T> { Some(value) }
	fn bind<U>(cb: fn(&T) -> Option<U>) -> Option<U> {
		match self {
			Some(value) => cb(&value),
			None => None
		}
	}
}

/*
monad.rs:8:1: 13:2 error: method `bind` has an incompatible type: expected trait Monad but found enum core::option::Option
monad.rs:8 	fn bind<U>(cb: fn(&T) -> Option<U>) -> Option<U> {
monad.rs:9 		match self {
monad.rs:10 			Some(value) => cb(&value),
monad.rs:11 			None => None
monad.rs:12 		}
monad.rs:13 	}
*/