58 lines
1.3 KiB
Rust
58 lines
1.3 KiB
Rust
// ==== main ==== //
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fn main() {
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let results =
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amb(&["the", "that", "a"]) >> move |a|
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amb(&["frog", "elephant", "thing"]) >> move |b|
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amb(&["walked", "treaded", "grows"]) >> move |c|
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amb(&["slowly", "quickly"]) >> move |d|
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assert(joins(a, b)) >> move |_|
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assert(joins(b, c)) >> move |_|
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assert(joins(c, d)) >> move |_|
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ret((a, b, c, d));
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for (a, b, c, d) in results {
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println!("{} {} {} {}", a, b, c, d);
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}
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}
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fn joins(x: &str, y: &str) -> bool {
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x.chars().last() == y.chars().next()
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}
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// ==== Amb ==== //
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struct Amb<T: Iterator>(T);
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impl<T: Iterator> IntoIterator for Amb<T> {
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type IntoIter = T;
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type Item = T::Item;
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fn into_iter(self) -> Self::IntoIter { self.0 }
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}
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impl<T, U, F> std::ops::Shr<F> for Amb<T>
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where
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T: Iterator,
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U: Iterator,
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F: FnMut(T::Item) -> Amb<U>,
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{
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type Output = Amb<std::iter::FlatMap<T, Amb<U>, F>>;
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fn shr(self, f: F) -> Self::Output {
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Self(self.0.flat_map(f))
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}
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}
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fn amb<I: IntoIterator>(i: I) -> Amb<I::IntoIter> {
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Amb(i.into_iter())
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}
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fn assert(x: bool) -> Amb<impl Iterator<Item = ()>> {
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Amb(std::iter::once(()).filter(move |_| x))
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}
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fn ret<T>(x: T) -> Amb<impl Iterator<Item = T>> {
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Amb(std::iter::once(x))
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}
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