See our previous discussion on this topic here: http://www.nabble.com/Fwd:-Unification-for-rank-N-types-td23942179.html Thanks, Vladimir On Wed, Oct 14, 2009 at 10:35 PM, Martijn van Steenbergen < martijn@van.steenbergen.nl> wrote:
Dear café,
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ImpredicativeTypes #-}
type Void = forall a. a
newtype Mono a = Mono { runMono :: [Void] }
beep :: Mono a -> Mono a beep (Mono vs) = Mono (map undefined vs)
Compiling this with GHC results in:
Monotype.hs:9:28:
Cannot match a monotype with `Void' Expected type: Void Inferred type: a
What does this error mean and why does the code not compile?
Thanks!
Martijn. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe