chore(i8n,learn): processed translations

curriculum/challenges/espanol/10-coding-interview-prep/rosetta-code/y-combinator.md

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+---
+id: 594810f028c0303b75339ad5
+title: Y combinator
+challengeType: 5
+forumTopicId: 302345
+dashedName: y-combinator
+---
+
+# --description--
+
+In strict [functional programming](https://en.wikipedia.org/wiki/Functional programming "wp: functional programming") and the [lambda calculus](https://en.wikipedia.org/wiki/lambda calculus "wp: lambda calculus"), functions (lambda expressions) don't have state and are only allowed to refer to arguments of enclosing functions. This rules out the usual definition of a recursive function wherein a function is associated with the state of a variable and this variable's state is used in the body of the function. The [Y combinator](https://mvanier.livejournal.com/2897.html) is itself a stateless function that, when applied to another stateless function, returns a recursive version of the function. The Y combinator is the simplest of the class of such functions, called [fixed-point combinators](https://en.wikipedia.org/wiki/Fixed-point combinator "wp: fixed-point combinator").
+
+# --instructions--
+
+Define the stateless Y combinator function and use it to compute [factorial](https://en.wikipedia.org/wiki/Factorial "wp: factorial"). The `factorial(N)` function is already given to you. **See also:**
+
+<ul>
+  <li><a href="https://vimeo.com/45140590" target="_blank">Jim Weirich: Adventures in Functional Programming</a>.</li>
+</ul>
+
+# --hints--
+
+Y should return a function.
+
+```js
+assert.equal(typeof Y((f) => (n) => n), 'function');
+```
+
+factorial(1) should return 1.
+
+```js
+assert.equal(factorial(1), 1);
+```
+
+factorial(2) should return 2.
+
+```js
+assert.equal(factorial(2), 2);
+```
+
+factorial(3) should return 6.
+
+```js
+assert.equal(factorial(3), 6);
+```
+
+factorial(4) should return 24.
+
+```js
+assert.equal(factorial(4), 24);
+```
+
+factorial(10) should return 3628800.
+
+```js
+assert.equal(factorial(10), 3628800);
+```
+
+# --seed--
+
+## --after-user-code--
+
+```js
+var factorial = Y(f => n => (n > 1 ? n * f(n - 1) : 1));
+```
+
+## --seed-contents--
+
+```js
+function Y(f) {
+  return function() {
+
+  };
+}
+
+var factorial = Y(function(f) {
+  return function (n) {
+    return n > 1 ? n * f(n - 1) : 1;
+  };
+});
+```
+
+# --solutions--
+
+```js
+var Y = f => (x => x(x))(y => f(x => y(y)(x)));
+```