That makes sense, thank you. Roman
* Simon Peyton-Jones <simo...@microsoft.com> [2013-03-21 08:25:03+0000] > Generally speaking ALL constraints (class constraints, equality constraints, > implicit parameters) range only over monotypes. > > The apparatus should extend to polymorphic types, be it's somewhat uncharted > territory. I doubt there'd be much problem in the case of implicit > parameters. > > In short, in principle it might be possible, but it would take a little > careful thought and I have too few careful-thought electrons available right > now. > > Simon > > | -----Original Message----- > | From: glasgow-haskell-users-boun...@haskell.org > [mailto:glasgow-haskell-users- > | boun...@haskell.org] On Behalf Of Roman Cheplyaka > | Sent: 20 March 2013 08:58 > | To: glasgow-haskell-users@haskell.org > | Subject: Polymorphic implicit parameters > | > | I'm curious as to why GHC doesn't accept the following (contrived) > | module: > | > | {-# LANGUAGE ImplicitParams, RankNTypes #-} > | > | f :: (?g :: (forall a . a -> a)) => a -> a > | f = ?g > | > | The error message is: > | > | Illegal polymorphic or qualified type: forall a. a -> a > | In the type signature for `f': > | f :: ?g :: (forall a. a -> a) => a -> a > | > | It's not a big deal since one can wrap the polymorphism in a newtype, > | but it's somewhat unexpected. > | > | Roman > | > | _______________________________________________ > | Glasgow-haskell-users mailing list > | Glasgow-haskell-users@haskell.org > | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users _______________________________________________ Glasgow-haskell-users mailing list Glasgow-haskell-users@haskell.org http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
