Editable

// Demo code (the actual new parser character stream implementation)
  
  function StringStream(string) {
    this.pos = 0;
    this.string = string;
  }
  
  StringStream.prototype = {
    done: function() {return this.pos >= this.string.length;},
    peek: function() {return this.string.charAt(this.pos);},
    next: function() {
      if (this.pos < this.string.length)
        return this.string.charAt(this.pos++);
    },
    eat: function(match) {
      var ch = this.string.charAt(this.pos);
      if (typeof match == "string") var ok = ch == match;
      else var ok = ch && match.test ? match.test(ch) : match(ch);
      if (ok) {this.pos++; return ch;}
    },
    eatWhile: function(match) {
      var start = this.pos;
      while (this.eat(match));
      if (this.pos > start) return this.string.slice(start, this.pos);
    },
    backUp: function(n) {this.pos -= n;},
    column: function() {return this.pos;},
    eatSpace: function() {
      var start = this.pos;
      while (/\s/.test(this.string.charAt(this.pos))) this.pos++;
      return this.pos - start;
    },
    match: function(pattern, consume, caseInsensitive) {
      if (typeof pattern == "string") {
        function cased(str) {return caseInsensitive ? str.toLowerCase() : str;}
        if (cased(this.string).indexOf(cased(pattern), this.pos) == this.pos) {
          if (consume !== false) this.pos += str.length;
          return true;
        }
      }
      else {
        var match = this.string.slice(this.pos).match(pattern);
        if (match && consume !== false) this.pos += match[0].length;
        return match;
      }
    }
  };

Editable

Output