#16135: Panic with ExistentialQuantification and ApplicativeDo -------------------------------------+------------------------------------- Reporter: Ashley | Owner: (none) Yakeley | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- {{{ {-# LANGUAGE ExistentialQuantification, ApplicativeDo #-} module Bug where data T f = forall a. MkT (f a) runf :: forall f. Functor f => IO (T f) runf = do return () MkT fa <- runf return $ MkT fa }}} {{{ Bug.hs:11:18: error:ghc: panic! (the 'impossible' happened) (GHC version 8.6.3 for x86_64-unknown-linux): No skolem info: [a_a1nb[ssk:2]] Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in ghc:Outputable pprPanic, called at compiler/typecheck/TcErrors.hs:2891:5 in ghc:TcErrors Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/16135 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler