Thank you very much, that does clarify things! Francesco Ariis wrote: That's correct! Indeed ghc is not complaining about a lack of instances, as it would with, say     λ> putStrLn 5     -- • No instance for (Num String) arising from etc etc. but about the *ambiguity* of type variable `e`.  How does `catch` know _which_ exception to deal with if you don't specify the concrete type? Consider:     prova = catch (print $ div (error "hey bby") 0)                   (\e -> print "ouch" >>                          print (e :: ErrorCall))     -- I want to deal with arithmetic errors here and not in `prova`     palla = catch prova                   (\e -> print "baaah" >>                          print (e :: ArithException)) If I switch ArithException and ErrorCall the behaviour of invoking `palla` changes. Having a catch-all `catch` is possible by using (e :: SomeException); if you don't care about `e` and just want to do an action regardless, you are probably better off with `onException`. Ask more if needed!