bug with rank n polymorphism in classes

[Simon Peyton-Jones]

I spoke too soon.  This is a real bug, and I'm fixing it.

Thanks for the report

S


| -----Original Message-----
| From: Hal Daume III [mailto:hdaume at ISI.EDU] 
| Sent: 01 September 2002 14:27
| To: Simon Peyton-Jones
| Cc: glasgow-haskell-bugs at haskell.org
| Subject: RE: bug with rank n polymorphism in classes
| 
| 
| 5.04 for solaris (but it doesn't seem to work in the linux 
| version, either).
| 
| --
| Hal Daume III
| 
|  "Computer science is no more about computers    | hdaume at isi.edu
|   than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume
| 
| On Wed, 28 Aug 2002, Simon Peyton-Jones wrote:
| 
| > Please say which version of GHC you are using.
| > 
| > This program works fine with GHC 5.02.2
| > 
| > Simon
| > 
| > | -----Original Message-----
| > | From: Hal Daume III [mailto:hdaume at ISI.EDU]
| > | Sent: 22 August 2002 20:47
| > | To: glasgow-haskell-bugs at haskell.org
| > | Subject: bug with rank n polymorphism in classes
| > | 
| > | 
| > | consider:
| > | 
| > | module Foo where
| > | 
| > | class Foo p where
| > |     foo :: p -> (forall q . Foo q => q -> a) -> a
| > | 
| > | instance Foo Int where
| > | 
| > | 
| > | if you load this in to ghci, it complains:
| > | 
| > | /home/hdaume/projects/NLP/Foo.hs:6:
| > |     Ambiguous type variable(s) `q' in the constraint `Foo q'
| > |     arising from a function with an overloaded argument type
| > | at /home/hdaume/projects/NLP/Foo.hs:6
| > | 	Expected type: Int -> (forall q1. (Foo q1) => q1 -> a) -> a
| > | 	Inferred type: Int -> (q -> a) -> a
| > |     In the application `GHC.Err.noMethodBindingError 
| > | "/home/hdaume/projects/NLP/Foo.hs:6|Foo.foo"#'
| > | 
| > | which is a reasonable complaint, but is emiited in a rather
| > | bizzare way.
| > | 
| > | --
| > | Hal Daume III
| > | 
| > |  "Computer science is no more about computers    | hdaume at isi.edu
| > |   than astronomy is about telescopes." -Dijkstra | 
| > | www.isi.edu/~hdaume
| > | 
| > | _______________________________________________
| > | Glasgow-haskell-bugs mailing list
| > | Glasgow-haskell-bugs at haskell.org 
| > | http://www.haskell.org/mailman/listinfo/glasgow-| haskell-bugs
| > | 
| > 
| 
|