Lex/Yacc are great for parsing things like your own internal files that the end-user never directly touches. But if you really care about your users, there are

Lex/Yacc are great for parsing things like your own internal files that the end-user never directly touches. But if you really care about your users, there are certain times when you've just gotta bite the bullet and hand-roll a parser. Because when the user mis-places a punctuation mark, it's much better to give them a humanly-thought-out human-readable error message rather than a generic blob of unreadable gibberish.