Data family quantification = GHC panic, ‘impossible’ happened
{-# Language RankNTypes #-}{-# Language TypeApplications #-}{-# Language PolyKinds #-}{-# Language KindSignatures #-}{-# Language TypeFamilies #-}datafamilyPair::foralla.forallb.*datainstancePair@a@b=MkPairab
$ ghci -ignore-dot-ghci 593_bug.hsGHCi, version 8.7.20181017: http://www.haskell.org/ghc/ :? for help[1 of 1] Compiling Main ( 593_bug.hs, interpreted )ghc-stage2: panic! (the 'impossible' happened) (GHC version 8.7.20181017 for x86_64-unknown-linux): ASSERT failed! kind axiom D:R:Pairabab0 :: forall a b (a :: a) (b :: b). Pair = R:Pairabab -- Defined at 593_bug.hs:8:15 forall k k (a :: k) (b :: k). * forall a b -> a -> b -> * 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/typecheck/FamInst.hs:158:61 in ghc:FamInstPlease report this as a GHC bug: http://www.haskell.org/ghc/reportabug>