Re: [Haskell-cafe] returning a polymorphic function

Hi. The most robust way to achieve this is to define

{-# LANGUAGE RankNTypes #-}

newtype PolyId = PolyId (forall a. a -> a)

f :: IO PolyId f = return (PolyId id)

main = do PolyId g <- f print $ g 1 print $ g "ciao"

You can also do this more directly using ImpredicativeTypes, but that language extension is quite fragile and not really supported. Cheers, Andres -- Andres Löh, Haskell Consultant Well-Typed LLP, http://www.well-typed.com