45 lines
1.1 KiB
Plaintext
45 lines
1.1 KiB
Plaintext
use std::sync::Arc;
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use std::boxed::Box;
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use std::clone::Clone;
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//Arc<Box<Closure>>
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#[macro_export]
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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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pub enum Mu<T> {
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Roll(Arc<Box<Fn(Mu<T>)->T>>),
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}
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pub fn unroll<T>(Mu::Roll(f): Mu<T>) -> Arc<Box<Fn(Mu<T>)->T>> {f.clone()}
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pub type Func<A, B> = Arc<Box<Fn(A)->B>>;
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pub type RecFunc<A, B> = Arc<Box<Fn(Func<A, B>) -> Func<A, B>>>;
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pub fn y<A, B>(f: RecFunc<A, B>) -> Func<A, B> {
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let g:Arc<Box<Fn(Mu<Func<A, B>>)->Func<A, B>>> = abc!(move |x : Mu<Func<A, B>>| -> Func<A, B> {
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let f = f.clone();
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abc!(move |a:A| -> B {
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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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#[test]
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fn fib_test() {
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let fib : RecFunc<i32, i32> = abc!(|f| abc!(move |x| if (x<2) { 1 } else { f(x-1) + f(x-2)}));
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let b = y(fib)(10);
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assert_eq!(b, 89);
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}
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#[test]
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fn fac_test() {
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let fac : RecFunc<i32, i32> = abc!(|f| abc!(move |x| if (x==0) { 1 } else { f(x-1) * x }));
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let c = y(fac)(10);
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assert_eq!(c, 3628800);
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}
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