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//@ run-pass
struct State;
type Error = ();
trait Bind<F> { //~ WARN trait `Bind` is never used
type Output;
fn bind(self, f: F) -> Self::Output;
}
fn bind<T, U, A, B, F>(mut a: A, mut f: F)
-> impl FnMut(&mut State) -> Result<U, Error>
where F: FnMut(T) -> B,
A: FnMut(&mut State) -> Result<T, Error>,
B: FnMut(&mut State) -> Result<U, Error>
{
move |state | {
let r = a(state)?;
f(r)(state)
}
}
fn atom<T>(x: T) -> impl FnMut(&mut State) -> Result<T, Error> {
let mut x = Some(x);
move |_| x.take().map_or(Err(()), Ok)
}
fn main() {
assert_eq!(bind(atom(5), |x| atom(x > 4))(&mut State), Ok(true));
}
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