#7536: Panic with TypeFamilies and FlexibleInstances
-------------------------------+--------------------------------------------
Reporter: snowleopard | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler
Version: 7.6.1 | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: Compile-time crash | Blockedby:
Blocking: | Related:
-------------------------------+--------------------------------------------
The code below brings GHC to panic.
{{{
{-# LANGUAGE TypeFamilies, FlexibleInstances #-}
module Bug where
type Node v = Int
class Predicate a where
type Var a
variable :: Var a -> a
instance Predicate (Node v) where
type Var (Node v) = v
variable = undefined
}}}
Panic details:
{{{
ghc: panic! (the 'impossible' happened)
(GHC version 7.4.2 for i386-unknown-mingw32):
tcTyVarDetails
( v{tv aa3} [tv] :: ghc-prim:GHC.Prim.*{(w) tc 34d} )
}}}
Can be reproduced on GHC versions 7.4.2 and 7.6.1.
Possibly, a duplicate of
[http://hackage.haskell.org/trac/ghc/ticket/7458], but difficult to tell
without additional info on the latter.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7536>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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