GHC Panic with QuantifiedConstraints
From branch wip/T2893
{-# Language QuantifiedConstraints #-}
{-# Language StandaloneDeriving #-}
{-# Language DataKinds #-}
{-# Language TypeOperators #-}
{-# Language GADTs #-}
{-# Language KindSignatures #-}
{-# Language FlexibleInstances #-}
{-# Language UndecidableInstances #-}
{-# Language MultiParamTypeClasses #-}
{-# Language RankNTypes #-}
{-# Language ConstraintKinds #-}
import Data.Kind
data D c where
D :: c => D c
newtype a :- b = S (a => D b)
class C1 a b
class C2 a b
instance C1 a b => C2 a b
class (forall xx. f xx) => Limit f
instance (forall xx. f xx) => Limit f
-- impl :: Limit (C1 a) :- Limit (C2 a)
-- impl = S D
infixr 5 :<
data Sig a = N a | a :< Sig a
data AST :: (Sig Type -> Type) -> (Sig Type -> Type) where
Sym :: dom a -> AST dom a
(:$) :: AST dom (xx :< a) -> AST dom (N xx) -> AST dom a
deriving instance (forall xx. Show (dom xx)) => Show (AST dom a)
data Arith a where
Plus :: Arith (Int :< Int :< N Int)
deriving instance Show (Arith a)
loading this program and evaluating Sym Plus
works fine:
$ ghc-stage2 --interactive hs/175-bug.hs
GHCi, version 8.5.20180128: http://www.haskell.org/ghc/ :? for help
[1 of 1] Compiling Main ( hs/175-bug.hs, interpreted )
Ok, one module loaded.
*Main> Sym Plus
Sym Plus
*Main>
but we uncomment impl
we get a panic!
GHCi, version 8.5.20180128: http://www.haskell.org/ghc/ :? for help
[1 of 1] Compiling Main ( hs/175-bug.hs, interpreted )
Ok, one module loaded.
*Main> Sym Plus
ghc-stage2: panic! (the 'impossible' happened)
(GHC version 8.5.20180128 for x86_64-unknown-linux):
nameModule
system df_a2VB
Call stack:
CallStack (from HasCallStack):
callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable
pprPanic, called at compiler/basicTypes/Name.hs:241:3 in ghc:Name
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
*Main>
Trac metadata
Trac field | Value |
---|---|
Version | 8.2.2 |
Type | Bug |
TypeOfFailure | OtherFailure |
Priority | normal |
Resolution | Unresolved |
Component | Compiler |
Test case | |
Differential revisions | |
BlockedBy | |
Related | |
Blocking | |
CC | |
Operating system | |
Architecture |