GADT pattern match in non-rigid context

[Isaac Dupree]

Neil Mitchell wrote:
> Hi Simon,
> 
>> You should be giving a type signature to rewrap!  That should fix it.
> 
> Thanks, all works fine now :-)

it would be great if the error message suggested giving a type signature 
as a solution (or maybe it already does, in the HEAD?)

Isaac

> 
> Neil
> 
>> | -----Original Message-----
>> | From: glasgow-haskell-users-bounces at haskell.org [mailto:glasgow-haskell-users-bounces at haskell.org] On Behalf Of
>> | Neil Mitchell
>> | Sent: 17 December 2007 16:23
>> | To: glasgow-haskell-users at haskell.org
>> | Subject: GADT pattern match in non-rigid context
>> |
>> | Hi,
>> |
>> | Upgrading from GHC 6.6 to 6.8 has caused some code to stop working:
>> |
>> | ----------------------------------------------------------------------
>> | {-# OPTIONS_GHC -fglasgow-exts #-}
>> |
>> | module Data2 where
>> |
>> | data CCompany
>> |
>> | data Paradise :: * -> * where
>> |     CC :: Paradise CCompany
>> |
>> | rewrapCC CC = []
>> | ----------------------------------------------------------------------
>> |
>> | [1 of 1] Compiling Data2            ( Data2.hs, interpreted )
>> |
>> | Data2.hs:12:9:
>> |     GADT pattern match in non-rigid context for `CC'
>> |       Tell GHC HQ if you'd like this to unify the context
>> |     In the pattern: CC
>> |     In the definition of `rewrapCC': rewrapCC CC = []
>> |
>> | This code is from the Uniplate benchmarking code, which runs the
>> | Paradise benchmark from SYB on Uniplate, Compos and SYB. The Compos
>> | code uses GADT's, so the program first needs to convert from standard
>> | data structures to GADT's before it can work, then back at the end.
>> | It's the problem of converting from a GADT to a normal data structure
>> | that is failing.
>> |
>> | So is there an easy workaround? Or should I be asking GHC HQ to unify things?
>> |
>> | Thanks
>> |
>> | Neil
>> | _______________________________________________
>> | Glasgow-haskell-users mailing list
>> | Glasgow-haskell-users at haskell.org
>> | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
>>
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