There's a catch: My reader code is in continuation-passing style, and if the input's too long, it goes into a stack overflow.

Fortunately, the reason it's in CPS is so that it can process the input asynchronously. As long as it's actually working asynchronously, its continuation callbacks occur on fresh event stacks rather than piling up. I could go into more details, but what's important is that for now, submitting the input in smaller pieces is an effective, if ugly, workaround:

  var arcArc = document.getElementsByTagName( "textarea" )[ 0 ].
      value.split( "\n" );
  function readRest() {
      if ( arcArc.length === 0 ) return;
      consoleIn.o.writeString( arcArc.shift() + "\n" );
      setTimeout( readRest, 0 );
  }
  readRest();

"Actually, if you you paste from Java Rainbow's arc.arc source yourself, you'll probably find that Rainbow.js encounters a stack overflow error. At this point it's necessary to enter it in more bite-size pieces. Right now you can accomplish this by pasting all of arc.arc into the input box, then entering the following code into a JavaScript console (not the Arc console!) to have it entered one line at a time:

[the JS code I pasted above]"

In Chrome, the JavaScript console is available under "(wrench icon) > Tools > JavaScript console." On Firefox, I tested it using Firebug's console tab, but I think the Error Console might work too.

Also, pasting the JavaScript snippet all at once should be fine. The point is to enter the Arc code in bite-size pieces, and the JavaScript snippet just automates that process.

Done! Now the reader only uses a number of JavaScript stack frames proportional to the amount of nesting of the program, rather than the number of characters. Feel free to just paste all of arc.arc into the REPL and hit enter. ^_^

I've also tested the REPL on more browsers. The only one that really had a problem was IE 8, and that was because of the code of the REPL interface itself rather than the Rainbow.js runtime. It should work in IE 8 now... except that the performance is terrible there. XD