INTERNAL ERROR: findBtyvsInt strikes again!

[Sigbjorn Finne]

Hi there,

thanks for a fine report. This has been fixed in the CVS sources,
but not in time for the Nov2003 release.

Notice that your code snippet depends on a feature of the
scoped type variable extension that's not supported by
Hugs (tyvars in the head of a class/instance decl being in scope);
see 7.4.10.2 of the GHC documentation:

  http://haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html

--sigbjorn

----- Original Message ----- 
From: "Alexandru D. Salcianu" <salcianu at MIT.EDU>
To: <hugs-bugs at haskell.org>
Sent: Thursday, November 20, 2003 16:40
Subject: INTERNAL ERROR: findBtyvsInt strikes again!


> 
> Hello!
> 
> I'm using Hugs (the November 2002 version) and I've encountered the
> "INTERNAL ERROR: findBtyvsInt" error.  I've read online that this
> error was known in the November 1999 version, but was fixed in the
> 2000 version.  I'm using the 2002 version and still get it.
> 
> I've encountered the error while working on a collection library (of
> course, I'm using the multi-parameter typeclass extension).
> 
> $ hugs -98
> __   __ __  __  ____   ___      _________________________________________
> ||   || ||  || ||  || ||__      Hugs 98: Based on the Haskell 98 standard
> ||___|| ||__|| ||__||  __||     Copyright (c) 1994-2002
> ||---||         ___||           World Wide Web: http://haskell.org/hugs
> ||   ||                         Report bugs to: hugs-bugs at haskell.org
> ||   || Version: November 2002  _________________________________________
> 
> Hugs mode: Restart with command line option +98 for Haskell 98 mode
> 
> Reading file "/usr/lib/hugs/lib/Prelude.hs":
>                    
> Hugs session for:
> /usr/lib/hugs/lib/Prelude.hs
> Type :? for help
> Prelude> :load Map.hs
> Reading file "Map.hs":
> Type checking      
> INTERNAL ERROR: findBtyvsInt
> Prelude> :version
> -- Hugs Version November 2002
> 
> Here is the content of Map.hs:
> 
> module Map where
> 
> -- objects of type ce represent sets of e's
> class (Eq e) => Set e ce | ce -> e where
>     equalSet  :: ce -> ce -> Bool
> 
> -- objects of type map represent maps from key to value
> class (Eq key) => FiniteMap key value map | map -> key value where
>     -- returns all keys from map, as a set of type keyset
>     mapKeys     :: (Set key keyset) => map -> keyset
> 
>     equalMap    :: map -> map -> Bool
>     {-- ERROR in this incomplete default implem. of equalMap --}
>     equalMap m1 m2 = 
>         let 
>             (keys1 :: [key]) = (mapKeys m1)
>             (keys2 :: [key]) = (mapKeys m2)
>         in
>             equalSet keys1 keys2
> 
> instance (Eq a) => Set a [a] where
>     equalSet = (==)
> 
> 
> (I've trimmed the code down to obtain a small bug report; the above
> code should be enough to trigger the error).  This code compiles fine
> with the GHC 6 (with the command line "ghc -c -fglasgow-exts Map.hs").
> 
> Best,
> 
> Alex