93 lines
2.0 KiB
Rust
93 lines
2.0 KiB
Rust
pub trait LensView<T> {
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type Field;
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fn view(thing: T) -> Self::Field;
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}
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pub trait LensOver<T>: LensView<T> {
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fn over(thing: T, f: &dyn Fn(Self::Field) -> Self::Field) -> T;
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fn set(thing: T, v: Self::Field) -> T {
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Self::over(thing, &|_| v)
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}
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}
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pub fn view<T, L: LensView<T>>(_lens: L, thing: T) -> L::Field {
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L::view(thing)
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}
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pub fn set<T, L: LensOver<T>>(_lens: L, thing: T, v: L::Field) -> T {
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L::set(thing, v)
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}
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pub fn over<T, L: LensOver<T>>(_lens: L, thing: T, f: &dyn Fn(L::Field) -> L::Field) -> T {
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L::over(thing, f)
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}
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// TODO add Fn implementation for lenses
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// with one param it should be view, with two it should be over
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// TODO add std::ops::Add to combine lenses
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// TODO add second_from_tuple, etc
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// TODO array traversals
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// TODO make over work with changing types
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pub mod lenses;
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#[cfg(test)]
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mod tests {
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use super::{lenses::_0, *};
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#[test]
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fn view_first_from_tuple() {
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let a = (1, 2);
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assert_eq!(view(_0, a), 1);
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// you can call it both ways
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let a = (1, 2);
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assert_eq!(_0::view(a), 1);
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let a = (1, 2);
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assert_eq!(view(_0, &a), &1);
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let mut a = (1, 2);
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assert_eq!(view(_0, &mut a), &mut 1);
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let a = (1, 2, 3);
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assert_eq!(view(_0, a), 1);
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let a = (1, 2, 3);
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assert_eq!(view(_0, &a), &1);
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}
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#[test]
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fn view_first_from_tuple_mut_works() {
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let mut a = (1, 2);
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*view(_0, &mut a) += 1;
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assert_eq!(a, (2, 2));
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}
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#[test]
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fn set_first_from_tuple() {
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let a = (1, 2);
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let a = set(_0, a, 3);
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assert_eq!(a, (3, 2));
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let a = (1, 2);
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let a = _0::set(a, 3);
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assert_eq!(a, (3, 2));
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}
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#[test]
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fn over_first_from_tuple() {
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let a = (1, 2);
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let a = over(_0, a, &|v| v + 1);
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assert_eq!(a, (2, 2));
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let a = (1, 2);
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let a = _0::over(a, &|v| v + 1);
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assert_eq!(a, (2, 2));
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}
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}
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