Dear all, I'd like to write a function "maybeShow :: a -> Maybe String", which runs "show" if its argument is of class Show. The context and motivation for this are as follows. I have a GADT type which encapsulates abstract-value computation (or constants or error codes), a snippet of which is below. data AV t where AVLeft :: AV a -> AV (Either a b) This is used to implement an arrow transformer, and due to Arrows mapping all Haskell functions, I cannot put some kind of qualification on the constructor, like "AVLeft :: Show a => ...". Of course any replies are welcome, but I do need something implemented and stable. If there are GHC-compatible hacks, even an "unsafeShow :: a -> String", that'd be great. I'd also prefer not to branch on all types which could possibly be maybeShow's argument. (Concretely, if I have "newtype AVFunctor a b c = AVF (a (AV b) (AV c))", then the Arrow class declaration forces all types, c.f. variable b, to be potential variables of type AV), class (Category a) => Arrow a where arr :: (b -> c) -> a b c Thanks very much, Nicholas — https://ntung.com — CS major @ UC Berkeley p.s. I posted this question on StackOverflow if you care to get brownie points there, http://goo.gl/PrmYW p.s. 2 -- if there is a general "dump var" function in ghci, which does more than ":info", I'd love to know :)