bad error message with GADTs

[Simon Peyton-Jones]

This is a bug, or at least infelicity, in 6.6.  I'm not inclined to fix it, unless something worse happens, because it's ok in the HEAD.

I will add a regression test though!

Simon


| -----Original Message-----
| From: glasgow-haskell-bugs-bounces at haskell.org [mailto:glasgow-haskell-
| bugs-bounces at haskell.org] On Behalf Of Donald Bruce Stewart
| Sent: 30 November 2006 00:38
| To: David Roundy
| Cc: glasgow-haskell-bugs at haskell.org
| Subject: Re: bad error message with GADTs
|
| droundy:
| > The following code gives a rather unpleasant error message with ghc
| 6.6.
| > Adding the type signature fixes the error.
| >
| > David
| >
| > {-# OPTIONS -fglasgow-exts #-}
| >
| > data PatchSeq p a b where
| >     Nil   :: PatchSeq p a a
| >     U  :: p a b -> PatchSeq p a b
| >     (:-)  :: PatchSeq p a b -> PatchSeq p b c -> PatchSeq p a c
| >
| > -- is_normal :: PatchSeq p a b -> Bool
| > is_normal Nil = True
| > is_normal (U _) = True
| > is_normal (U _ :- _) = True
| > is_normal _ = False
| > _______________________________________________
|
| I.e. this one?
|
| A.hs:9:10:
|     Couldn't match kind `?' against `* -> * -> *'
|     When matching the kinds of `t :: ?' and `t1 :: * -> * -> *'
|       Expected type: t1
|       Inferred type: t
|     In the pattern: Nil
|
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