Which means that this CAN NOT BE USED TO ACCEPT REGULAR LANGUAGES. The language (a|b)*, any number of as or bs in any order, can not be descibed using that pars

Which means that this CAN NOT BE USED TO ACCEPT REGULAR LANGUAGES. The language (a|b)*, any number of as or bs in any order, can not be descibed using that parser. "considerable simplification" sounds like it's kinda regex. It's not even basic regular expressions/regular languages. Edit: The author reimplements code from https://www.cs.princeton.edu/courses/archive/spr09/cos333/beautiful.html https://www.cs.princeton.edu/courses/archive/spr09/cos333/be... which acknowledges that the implemented subset does not match all classes but they propose that the classes they can parse, are already useful. The author of the new article makes no such acknowledgement that their implementation just represents a subset of regular languages. Of course, the regular languages themselves are also just a subset of regexp, which can match more languages due to constructs like references.