50 lines
1.1 KiB
Plaintext
50 lines
1.1 KiB
Plaintext
use std::sync::Arc;
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//Arc<Box<Closure>>
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macro_rules! abc {
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($x:expr) => (Arc::new(Box::new($x)));
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}
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#[derive(Clone)]
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enum Mu<T> {
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Roll(Arc<Box<Fn(Mu<T>)->T>>),
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}
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fn unroll<T>(Mu::Roll(f): Mu<T>) -> Arc<Box<Fn(Mu<T>)->T>> {f.clone()}
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pub type Func<A> = Arc<Box<Fn(A)->A>>;
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pub type RecFunc<A> = Arc<Box<Fn(Func<A>) -> Func<A>>>;
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pub fn y<A: 'static>(f: RecFunc<A>) -> Func<A> {
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let g: Arc<Box<Fn(Mu<Func<A>>)->Func<A>>> = abc!(move |x : Mu<Func<A>>| -> Func<A> {
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let f = f.clone();
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abc!(move |a:A| -> A {
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let f = f.clone();
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f(unroll(x.clone())(x.clone()))(a)
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})
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});
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g(Mu::Roll(g.clone()))
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}
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#[macro_export]
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macro_rules! y {
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(|$name:ident| $fun:tt) => {
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y(abc!(|$name| abc!($fun)))
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}
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}
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fn fac(n: u32) -> u32 {
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let fn_: Func<u32> = y!(|f| (move |x| if x == 0 { 1 } else { f(x-1) * x }));
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fn_(n)
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}
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fn fib(n: u32) -> u32 {
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let fn_: Func<u32> = y!(|f| (move |x| if x < 2 { x } else { f(x-1) + f(x-2) }));
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fn_(n)
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}
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fn main() {
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println!("{}", fac(10));
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println!("{}", fib(10))
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}
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