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/// Fixpoint combinator for rust closures, generalized over the return type. /// /// **Note:** Use this best through the [`fix`](fn.fix.html) function. /// /// In **Fix\<T, R\>**, **T** is the argument type, and **R** is the return type, /// **R** defaults to **T**. /// /// Calling the `Fix` value only supports function call notation with the nightly /// channel and the crate feature ‘unstable’ enabled; use the .call() method otherwise. /// /// ``` /// use odds::Fix; /// use odds::fix; /// /// let c = |f: Fix<i32>, x| if x == 0 { 1 } else { x * f.call(x - 1) }; /// let fact = Fix(&c); /// assert_eq!(fact.call(5), 120); /// /// let data = [true, false]; /// assert!(!fix(&data[..], |f, x| { /// x.len() == 0 || x[0] && f.call(&x[1..]) /// })); /// /// ``` #[cfg_attr(feature="unstable", doc=" ``` // using feature `unstable` use odds::Fix; let c = |f: Fix<i32>, x| if x == 0 { 1 } else { x * f(x - 1) }; let fact = Fix(&c); assert_eq!(fact(5), 120); ``` " )] pub struct Fix<'a, T: 'a, R: 'a = T>(pub &'a Fn(Fix<T, R>, T) -> R); /// Fixpoint combinator for rust closures, generalized over the return type. /// /// This is a wrapper function that uses the `Fix` type. The recursive closure /// has two arguments, `Fix` and the argument type `T`. /// /// In **Fix\<T, R\>**, **T** is the argument type, and **R** is the return type, /// **R** defaults to **T**. /// /// Calling the `Fix` value only supports function call notation with the nightly /// channel and the crate feature ‘unstable’ enabled; use the .call() method otherwise. /// /// This helper function makes the type inference work out well. /// /// ``` /// use odds::fix; /// /// assert_eq!(120, fix(5, |f, x| if x == 0 { 1 } else { x * f.call(x - 1) })); /// /// let data = [true, false]; /// assert!(!fix(&data[..], |f, x| { /// x.len() == 0 || x[0] && f.call(&x[1..]) /// })); /// /// ``` #[cfg_attr(feature="unstable", doc=" ``` // using feature `unstable` use odds::fix; assert_eq!(120, fix(5, |f, x| if x == 0 { 1 } else { x * f(x - 1) })); ``` " )] pub fn fix<T, R, F>(init: T, closure: F) -> R where F: Fn(Fix<T, R>, T) -> R { Fix(&closure).call(init) } impl<'a, T, R> Fix<'a, T, R> { /// Call the fix using the argument `arg` pub fn call(&self, arg: T) -> R { let f = *self; f.0(f, arg) } } impl<'a, T, R> Clone for Fix<'a, T, R> { fn clone(&self) -> Self { *self } } impl<'a, T, R> Copy for Fix<'a, T, R> { } #[cfg(feature="unstable")] impl<'a, T, R> FnOnce<(T,)> for Fix<'a, T, R> { type Output = R; #[inline] extern "rust-call" fn call_once(self, x: (T,)) -> R { self.call(x.0) } } #[cfg(feature="unstable")] impl<'a, T, R> FnMut<(T,)> for Fix<'a, T, R> { #[inline] extern "rust-call" fn call_mut(&mut self, x: (T,)) -> R { self.call(x.0) } } #[cfg(feature="unstable")] impl<'a, T, R> Fn<(T,)> for Fix<'a, T, R> { #[inline] extern "rust-call" fn call(&self, x: (T,)) -> R { self.call(x.0) } }