Y.js - mozsearch

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/* This Source Code Form is subject to the terms of the Mozilla Public

 * License, v. 2.0. If a copy of the MPL was not distributed with this

 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// The Y combinator, applied to the factorial function.

// Return the function that is the fixed point of f.

const Y = f => (x => f(v => x(x)(v)))

               (x => f(v => x(x)(v)));

// The factorial function is the fixed point of this:

const f = fac => n => (n <= 1) ? 1 : n * fac(n - 1);

print(`5! is ${Y(f)(5)}`);