GADT pattern match in non-rigid context

[Simon Peyton-Jones]

You should be giving a type signature to rewrap!  That should fix it.

Simon

| -----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
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