#2417: using GADT syntax for an associated datatype causes GHC to panic
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Reporter: guest | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 6.9 | Severity: minor
Keywords: | Testcase:
Architecture: Unknown | Os: Unknown
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I am aware that this is probably not supposed to be supported.
But even if using a GADT as an associated datatype instance
does not directly work, it would be nice if
* the GADT syntax was supported for "normal"
associated datatypes,
* the error message was more informative.
Example program:
{{{
{-# LANGUAGE TypeFamilies, GADTs #-}
class X a where
data T a
instance X Int where
data T Int where
C :: T Int
}}}
Error message:
{{{
ghc-6.9.20080615: panic! (the 'impossible' happened)
(GHC version 6.9.20080615 for x86_64-unknown-linux):
Maybe.fromJust: Nothing
}}}
Occurs with recent snapshot, but also with 6.8.2 and 6.8.3.
Andres
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2417>
GHC <http://www.haskell.org/ghc/>
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