我承认，我被绕进去了。
// The Y combinator, applied to the factorial function
// https://javascriptlint.svn.sourceforge.net/svnroot/javascriptlint/trunk/spidermonkey/src/Y.js
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));
// expand
Y(factorial)(5)
inner(inner)(5)
factorial(apply)(5)
(function (n) {
return (n <= 1) ? 1 : n * proc(n-1);
})(5) // proc = apply
5 * apply(4)
5 * factorial(apply)(4)
5 * (function (n) {
return (n <= 1) ? 1 : n * proc(n-1);
})(4)
5 * (4 * apply(3))
