Writing Scheme in Javascript I

Published: February 10, 2008 • Read time: 2 min read min

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) <graphic> "sally likes harry"
secret <graphic> Error: variable secret is not bound
*/
</graphic></graphic>

<?xml version="1.0" ?>
<graphic>
  <graphic>//the Javascript version of the same function
</graphic>
</graphic>

<?xml version="1.0" ?>
<graphic>
  <graphic>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() );</graphic>
</graphic>