#14154: Some cocktail of features causes GHC panic -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * cc: RyanGlScott (added) * version: 8.3 => 8.0.1 Old description:
{{{#!hs {-# Language RankNTypes, DerivingStrategies, TypeApplications, ScopedTypeVariables, GADTs, PolyKinds #-}
module T14154 where
newtype Ran g h a = MkRan (forall b. (a -> g b) -> h b)
newtype Swap p f g a where MkSwap :: p g f a -> Swap p f g a
ireturn :: forall m i a. a -> m i i a ireturn = undefined
xs = case ireturn @(Swap Ran) 'a' of MkSwap (MkRan f) -> f print }}}
{{{ $ ghci -ignore-dot-ghci /tmp/bug.hs GHCi, version 8.3.20170605: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/bug.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.3.20170605 for x86_64-unknown-linux): piResultTy k0_a1Ki[tau:2] b0_a1Kt[tau:2] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:949:35 in ghc:Type
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}}
New description: {{{#!hs {-# Language RankNTypes, TypeApplications, ScopedTypeVariables, GADTs, PolyKinds #-} module T14154 where newtype Ran g h a = MkRan (forall b. (a -> g b) -> h b) newtype Swap p f g a where MkSwap :: p g f a -> Swap p f g a ireturn :: forall m i a. a -> m i i a ireturn = undefined xs = case ireturn @(Swap Ran) 'a' of MkSwap (MkRan f) -> f print }}} {{{ $ ghci -ignore-dot-ghci /tmp/bug.hs GHCi, version 8.3.20170605: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /tmp/bug.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.3.20170605 for x86_64-unknown-linux): piResultTy k0_a1Ki[tau:2] b0_a1Kt[tau:2] Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1133:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1137:37 in ghc:Outputable pprPanic, called at compiler/types/Type.hs:949:35 in ghc:Type Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}} -- Comment: Interesting! This appears to be an old bug, since it happens all the way back in GHC 8.0.1 (that's as far back as I can go, since `TypeApplications` didn't exist before then). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14154#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler