The js-abstract-descent-parser from ericbn

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just a thanks for your youtube video on parsing

it is greatly appreciated.

The index is handled differently when handling characters as opposed to regular expressions

I've rewritten your regexp() method a little but it is essentially the same. It goes:

parseRegExp(regexp) {
  var parsed = false,
      inputLength = this.input.length;

  if (this.index < inputLength) {
    var inputSubstring = this.input.substr(this.index),
        matches = regexp.exec(inputSubstring);

    if (matches && matches.index === 0) {
      var firstMatch = first(matches),
          firstMatchLength = firstMatch.length;

      this.index += firstMatchLength;

      parsed = true;
    }
  }

  return parsed;
}

Here the index is only changed if there is a match. On the other hand, your char() method goes:

parseCharacter(character) {
  var parsed = false,
      inputLength = this.input.length;

  if (this.index < inputLength) {
    var inputCharacter = this.input.charAt(this.index);

    this.index += 1;

    if (inputCharacter === character) {
      parsed = true;
    }
  }

  return parsed;
}

Here the index is changed regardless of whether there is a match or not. I think it should be as follows:

parseCharacter(character) {
  var parsed = false,
      inputLength = this.input.length;

  if (this.index < inputLength) {
    var inputCharacter = this.input.charAt(this.index);

    if (inputCharacter === character) {
      this.index += 1;

      parsed = true;
    }
  }

  return parsed;
}

After all the char(...) method is a simplified regexp(...) method for all intents and purposes. Should it not behave in exactly the same way as far as the rest of the parse functionality is concerned? If I change the functionality, all your tests still pass.

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