Eddie Welker.com

This is an interesting little function that I ran across in Kent Dybvig’s The Scheme Programming Language. I thought I would give it a go in javascript. I wrote it out, and ran into two problems. First, I wasn’t returning anything from the anonymous-self-executing function, so it was being garbage collected, and the call to tell() would give an undefined (secret didn’t exist anymore). The second was that I initially declared secret without the var which gave it global scope. Took me a little while to figure these out, but since I haven’t looked at any javascript in months, I don’t feel so bad.

/* the original function from The Scheme Programming Language
(define shhh #f)
(define tell #f)

(let ((secret 0))
  (set! shhh
    (lambda (message)
      (set! secret message)))
  (set! tell
    (lambda ()
      secret)))

(shhh "sally likes harry")
(tell)  "sally likes harry"
secret  Error: variable secret is not bound
*/

//the Javascript version of the same function

var shhh = false;
var tell = (function(){
 var secret = 0;
 shhh = function(message) { secret = message; }
 return function() { console.info(secret); }
})();

shhh("harry likes sally");
console.info("tell: " + tell() );