#15625: GHC panic, with QuantifiedConstraints -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1-beta1 Keywords: | Operating System: Unknown/Multiple QuantifiedConstraints | Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I got a GHC Panic (I made some minor changes to GHC so it may have been added by me) but I think it's caused by the quality constraint {{{ $ ~/code/latestghc/inplace/bin/ghc-stage2 --interactive -ignore-dot-ghci ~/hs/390.hs GHCi, version 8.7.20180828: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( /home/baldur/hs/390.hs, interpreted ) ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.7.20180828 for x86_64-unknown-linux): ASSERT failed! co_a2DG df_a2DS @ Any Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable pprPanic, called at compiler/utils/Outputable.hs:1219:5 in ghc:Outputable assertPprPanic, called at compiler/coreSyn/CoreSubst.hs:189:49 in ghc:CoreSubst Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
}}} given this code {{{#!hs {-# Language RankNTypes, TypeInType, DataKinds, PolyKinds, TypeOperators, GADTs, FlexibleInstances, MultiParamTypeClasses, ConstraintKinds, CPP, UndecidableSuperClasses, QuantifiedConstraints, FlexibleContexts #-} import Data.Kind type Cat ob = ob -> ob -> Type data KLEISLI (m :: Type -> Type) :: Cat (KL_kind m) where MkKLEISLI :: (a -> m b) -> KLEISLI(m) (KL a) (KL b) data KL_kind (m :: Type -> Type) = KL Type class (a ~ KL xx) => AsKL a xx instance (a ~ KL xx) => AsKL a xx ekki__ :: Monad m => (forall xx. AsKL a xx) => KLEISLI m a a ekki__ = MkKLEISLI undefined }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15625 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler