For simple languages, it can be a bit of a pain to write and maintain a lexer and a parser. For example, if I'm gonna parse JSON and nothing more, I think it's a bit silly to use a two external DSLs when I could use a simple eDSL. I think Happy and Alex both have their places, absolutely. For parsing full on programming languages I can imagine using parser combinators to be a bit painful. But parser combinators work great for a lot of cases.