bug with rank n polymorphism in classes

[Hal Daume III]

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
> | 
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>