108 lines
2.6 KiB
Rust
108 lines
2.6 KiB
Rust
//@ known-bug: #121575
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// ignore-tidy-linelength
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#![feature(generic_const_exprs)]
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use std::array;
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trait PrimRec<const N: usize, const O: usize> {
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fn eval(&self, x: [usize; N]) -> [usize; O];
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}
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struct Zero;
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impl<const N: usize> PrimRec<N, 1> for Zero {
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fn eval(&self, _: [usize; N]) -> [usize; 1] {
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[0]
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}
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}
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struct Const(usize);
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impl<const N: usize> PrimRec<N, 1> for Const {
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fn eval(&self, _: [usize; N]) -> [usize; 1] {
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[self.0]
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}
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}
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struct S;
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impl PrimRec<1, 1> for S {
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fn eval(&self, x: [usize; 1]) -> [usize; 1] {
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[x[0] + 1]
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}
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}
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struct Proj<const I: usize>;
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impl<const N: usize, const I: usize> PrimRec<N, 1> for Proj<I> {
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fn eval(&self, x: [usize; N]) -> [usize; 1] {
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[x[I]]
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}
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}
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struct Merge<const N: usize, const O1: usize, const O2: usize, A: PrimRec<N, O1>, B: PrimRec<N, O2>>(
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A,
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B,
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);
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fn concat<const M: usize, const N: usize>(a: [usize; M], b: [usize; N]) -> [usize; M + N] {
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array::from_fn(|i| if i < M { a[i] } else { b[i - M] })
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}
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impl<const N: usize, const O1: usize, const O2: usize, A: PrimRec<N, O1>, B: PrimRec<N, O2>>
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PrimRec<N, { O1 + O2 }> for Merge<N, O1, O2, A, B>
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{
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fn eval(&self, x: [usize; N]) -> [usize; O1 + O2] {
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concat(self.0.eval(x), self.1.eval(x))
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}
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}
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struct Compose<const N: usize, const I: usize, const O: usize, A: PrimRec<N, I>, B: PrimRec<I, O>>(
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A,
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B,
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);
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impl<const N: usize, const I: usize, const O: usize, A: PrimRec<N, I>, B: PrimRec<I, O>>
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PrimRec<N, O> for Compose<N, I, O, A, B>
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{
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fn eval(&self, x: [usize; N]) -> [usize; O] {
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self.1.eval(self.0.eval(x))
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}
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}
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struct Rec<const N: usize, const O: usize, Base: PrimRec<N, O>, F: PrimRec<{ O + (N + 1) }, O>>(
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Base,
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F,
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);
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fn tail<const N: usize>(x: [usize; N + 1]) -> [usize; N] {
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array::from_fn(|i| x[i + 1])
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}
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fn cons<const N: usize>(x: usize, xs: [usize; N]) -> [usize; N + 1] {
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array::from_fn(|i| if i == 0 { x } else { xs[i - 1] })
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}
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impl<const N: usize, const O: usize, Base: PrimRec<N, O>, F: PrimRec<{ O + (N + 1) }, O>>
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PrimRec<{ N + 1 }, O> for Rec<N, O, Base, F>
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{
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fn eval(&self, x: [usize; N + 1]) -> [usize; O] {
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match (x[0], tail(x)) {
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(0, x) => self.0.eval(x),
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(y, x) => {
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let xy = cons(y - 1, x);
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let input = concat(self.eval(xy), xy);
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self.1.eval(input)
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}
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}
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}
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}
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fn main() {
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let one = Compose(Zero, S);
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dbg!(one.eval([]));
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let add: Rec<1, 1, Proj<0>, Compose<3, 1, 1, Proj<0>, S>> =
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Rec(Proj::<0>, Compose(Proj::<0>, S));
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dbg!(add.eval([3, 2]));
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}
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