[Haskell-cafe] Re: Translating perl -> haskell, string "fill ins" with an error on invalid inputseems awfullycomplex. Is there a way to simplify?

[Thomas Hartman]

 Claus and Evan ++; that was very helpful.

 FWIW, my gut feeling is that Claus's first version was easier to
 understand than the revision with printf, which seems to me to involve
 a lot more monadic wizardry (Functor, MonadError, fmap, mapm). The
 first version, which just used maybe, was clear to me within seconds.

 But again, I learned a lot. Thanks.