LFe tutorial 19 - message passing

lfe-tut-19.lfe

(defmodule lfe-tut-19
  (export (start 0)
          (ping 2)
          (pong 0)))

(defun ping
  ([0 pong-pid]
   (! pong-pid 'finished)
   (lfe_io:format "ping finished~n" ()))
  ([n pong-pid]
   (! pong-pid (tuple 'ping (self)))
   (receive
     ('pong
      (lfe_io:format "ping received pong~n" ())))
   (ping (- n 1) pong-pid)))

(defun pong []
  (receive
    ('finished
     (lfe_io:format "pong received finished, pong finished~n" ()))
    ((tuple 'ping ping-pid)
     (lfe_io:format "pong received ping~n" ())
     (! ping-pid 'pong)
     (pong))))

(defun start []
  (let ((pong-pid (spawn 'lfe-tut-19 'pong ())))
    (spawn 'lfe-tut-19 'ping (list 3 pong-pid))))