Y combinator in JS.

js/src/Y.js

@@ -0,0 +1,19 @@
+// The Y combinator, applied to the factorial function
+
+function factorial(proc) {
+    return function (n) {
+	return (n <= 1) ? 1 : n * proc(n-1);
+    }
+}
+
+function Y(outer) {
+    function inner(proc) {
+	function apply(arg) {
+	    return proc(proc)(arg);
+	}
+	return outer(apply);
+    }
+    return inner(inner);
+}
+
+print("5! is " + Y(factorial)(5));