#2787: Panic (core lint failure) with type synonym in GHC 6.10.1
---------------------------+------------------------------------------------
Reporter: BenMoseley | Owner:
Type: bug | Status: new
Priority: normal | Component: Compiler (Type checker)
Version: 6.10.1 | Severity: major
Keywords: | Testcase:
Architecture: x86 | Os: Windows
---------------------------+------------------------------------------------
This causes a panic:
{{{
{-# LANGUAGE TypeFamilies, GADTs #-}
module GHCBug (
PVR(..),
Core(..),
analyseCore
)
where
data Core a where Ctr :: Core Double
data PVR a = PVR a deriving (Eq, Show)
class Sub a where
type AssocSyn a :: * -> *
instance Sub Double where
type AssocSyn Double = PVR
analyseCore :: Core a -> ((AssocSyn a) a)
analyseCore Ctr = pvr
where
-- GHC panics if we use the below as the type sig for 'pvr'
pvr :: PVR ~ AssocSyn a => (AssocSyn a) a
-- pvr :: (AssocSyn a) a
pvr = undefined
main :: IO ()
main = print "ok"
}}}
The basic compiler panic is:
{{{
c:/ws/main/depot/QA/EDG/EDG_priv/FPF_Dev.br/src $ ghc -main-is GHCBug
~/GHCBug.hs
ghc.exe: panic! (the 'impossible' happened)
(GHC version 6.10.1 for i386-unknown-mingw32):
initC: srt_lbl
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}}
The core lint failure part is:
{{{
*** Checking old interface for main:GHCBug:
*** Parser:
*** Renamer/typechecker:
*** Desugar:
Result size = 199
*** Core Lint Errors: in result of Desugar ***
{-# LINE 21 "F:\ME\GHCBug.hs #-}:
[RHS of pvr_awa :: GHCBug.AssocSyn
GHC.Types.Double GHC.Types.Double]
pvr_afN is out of scope
*** Offending Program ***
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2787>
GHC <http://www.haskell.org/ghc/>
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