30 lines
938 B
Rust
30 lines
938 B
Rust
use super::*;
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pub enum Selected<'a, A: 'a, B: 'a, T: ?Sized + WeakFunctor<'a>> {
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A(A, T::F<B>),
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B(T::F<A>, B),
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}
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/// See [`ApplicativeSelect::select`].
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pub type SelectedWrapped<'a, A, B, T> = Wrap<'a, Selected<'a, A, B, T>, T>;
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/// Part of [`Applicative`] responsible for choosing the first value.
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pub trait ApplicativeSelect<'a>: Functor<'a> {
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fn select<A: 'a, B: 'a>(fa: Self::F<A>, fb: Self::F<B>) -> SelectedWrapped<'a, A, B, Self> {
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Self::fmap(fa, |a| Selected::A(a, fb))
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}
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}
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pub trait ApplicativeSelectExt<'a>: ApplicativeSelect<'a> {
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/// Shorthand for [`Functor::fmap`]∘[`ApplicativeSelect::select`].
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fn select_map<A: 'a, B: 'a, C: 'a>(
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fa: Self::F<A>,
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fb: Self::F<B>,
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f: impl 'a + FnOnce(Selected<'a, A, B, Self>) -> C,
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) -> Self::F<C> {
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Self::fmap(Self::select(fa, fb), f)
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}
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}
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impl<'a, T: ApplicativeSelect<'a>> ApplicativeSelectExt<'a> for T {}
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