Bluish Coder

Programming Languages, Martials Arts and Computers. The Weblog of Chris Double.


2006-04-27

Javascript Partial Continuations

I've been playing around with Rhino, a Javascript interpreter written in Java, using it as a server side scripting language. Rhino supports continuations so I thought I'd try and port the bshift and breset implementation I ported to Factor to Javascript.

My initial attempt is in partial-continuations.js.This can be loaded into the Rhino interpreter using:

load("partial-continuations.js")

Rhino's 'load' understands URL's so you can even do:

load("http://www.bluishcoder.co.nz/code/partial-continuations.js")

A simple use of the 'range' example in Javascript is:

function range(rc, from, to) {
 return  bshift(rc, function(pcc) {
               while(from <= to) {
                 pcc(from++);
               }
               return undefined;
             });

function test1() {
  breset(function(rc) { 
    print(range(rc, 1, 5)); 
    return 0; 
  });
}

This works fine printing the number from 1 to 5. I've struck a bit of wierdness with the attempt to translate the CLU-iterator idiom mentioned in my previous post. My Javascript translation was:

function test3() {
  var sum = 0;
  breset(function(rc) {
    var tmp = range(rc, 1, 10);
    sum += tmp;
  });
  print(sum);
}

This works, printing '55'. But if I change it to the following it prints 10:

function test3() {
  var sum = 0;
  breset(function(rc) {
    sum += range(rc, 1, 10);
  });
  print(sum);
}

For some reason the range call is not calling the entire breset scope. It's only calling from the 'range' onwards. Can anyone spot what's wrong with my implementation?

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