Joe Armstrong's Favorite Erlang Program... in LFE

joes-fav.lfe

(defmodule joes-fav
  (export all))

(defun universal-server ()
  (receive
    ((tuple 'become server-function)
     (funcall server-function))))

(defun factorial
  ((0) 1)
  ((number) (* number (factorial (- number 1)))))

(defun factorial-server ()
  (receive
    ((tuple sender number)
     (! sender (factorial number))
     (factorial-server))))

(defun run-it ()
  (let ((pid (spawn #'universal-server/0)))
    (! pid (tuple 'become #'factorial-server/0))
    (! pid (tuple (self) 50)))
  (receive
    (data data)))

run-it.lfe

> (run-it)
30414093201713378043612608166064768844377641568960512000000000000

sanity-check.lfe

> (slurp '"examples/joes-fav.lfe")
#(ok joes-fav)
> (factorial 10)
3628800
> (factorial 20)
2432902008176640000
> (factorial 50)
30414093201713378043612608166064768844377641568960512000000000000