Parsing to execute is easy. Real time parsing to do syntax highlighting and indenting less so. By convention people often implement some forms differently than

Parsing to execute is easy. Real time parsing to do syntax highlighting and indenting less so. By convention people often implement some forms differently than others. It isn't a crazy challenge, but the bar is higher than counting parens. And obviously Emacs doesn't do this correctly because it dies if someone throws a long line at it (the usual implementation of syntax highlighter is apparently regexp soup).