39 lines
1.1 KiB
Rust
39 lines
1.1 KiB
Rust
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// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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struct State;
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type Error = ();
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trait Bind<F> {
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type Output;
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fn bind(self, f: F) -> Self::Output;
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}
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fn bind<T, U, A, B, F>(mut a: A, mut f: F)
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-> impl FnMut(&mut State) -> Result<U, Error>
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where F: FnMut(T) -> B,
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A: FnMut(&mut State) -> Result<T, Error>,
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B: FnMut(&mut State) -> Result<U, Error>
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{
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move |state | {
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let r = a(state)?;
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f(r)(state)
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}
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}
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fn atom<T>(x: T) -> impl FnMut(&mut State) -> Result<T, Error> {
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let mut x = Some(x);
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move |_| x.take().map_or(Err(()), Ok)
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}
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fn main() {
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assert_eq!(bind(atom(5), |x| atom(x > 4))(&mut State), Ok(true));
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}
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