js/src/Y.js

   1 // The Y combinator, applied to the factorial function
   2
   3 function factorial(proc) {
   4     return function (n) {
   5         return (n <= 1) ? 1 : n * proc(n-1);
   6     }
   7 }
   8
   9 function Y(outer) {
  10     function inner(proc) {
  11         function apply(arg) {
  12             return proc(proc)(arg);
  13         }
  14         return outer(apply);
  15     }
  16     return inner(inner);
  17 }
  18
  19 print("5! is " + Y(factorial)(5));