#7474: Panic with zonkQuantifiedTyVar in GHC 7.6.1
-----------------------------+----------------------------------------------
Reporter: spl | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 7.6.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: None/Unknown | Blockedby:
Blocking: | Related:
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In GHC 7.6.1, the following code:
{{{
{-# LANGUAGE TypeFamilies, GADTs, FlexibleContexts, MultiParamTypeClasses
#-}
type family T :: * -> *
data E :: * -> * where
E :: C p => T (T p) -> E p
class C' b a where c :: T b -> a
class C' (T a) a => C a
-- f :: C' (T p) a => E p -> a
f (E d) = c d
}}}
produces the following error message:
{{{
[1 of 1] Compiling Main ( Test.hs, interpreted )
ghc: panic! (the 'impossible' happened)
(GHC version 7.6.1 for i386-apple-darwin):
zonkQuantifiedTyVar
<<details unavailable>>
}}}
Uncommented the type signature allows it to compile.
The code above '''does not''' panic in HEAD, so I guess it's fixed. But I
thought it would be good to report it anyway.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7474>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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