That makes sense, thank you.
Roman
* Simon Peyton-Jones
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-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@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