Allowing partially applied type synonyms amounts to allowing lambda at the type level, and that requires higher-order unification, and loses principal types (I think). So as of today, they are definitely out.
If you look at the paper about "boxy types" on my home page, you'll see ways of extending type inference to support higher rank types and impredicativity. Next on the list is lambdas at the type level, in the same spirit: that is, support type inference by asking the programmer to help at "key moments". But don't hold your breath. Simon | -----Original Message----- | From: [EMAIL PROTECTED] [mailto:glasgow-haskell-users- | [EMAIL PROTECTED] On Behalf Of Conal Elliott | Sent: 19 April 2005 05:21 | To: glasgow-haskell-users@haskell.org | Subject: Partial application of type constructors? | | GHC 6.4 objects to the following simple program, pointing to the partial | application of the type constructor AddL. Is there a work-around? | | {-# OPTIONS -fglasgow-exts #-} | data LMap a b | type AddL arr a b = a `arr` LMap a b | data DFunA arr a b = DFunA (a `arr` b) (DFunA (AddL arr) a b) | | The complete error message: | | Type synonym `AddL' should have 3 arguments, but has been given 1 | When checking the data constructor: | forall arr a b. DFunA (arr a b) (DFunA (AddL arr) a b) | In the data type declaration for `DFunA' | | Is there a serious difficulty with handling partial type applications? | | - Conal | | _______________________________________________ | 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
