#11334: GHC panic when calling typeOf on a promoted data constructor -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: Type: bug | Status: new Priority: high | Milestone: 8.0.1 Component: Compiler (Type | Version: 8.1 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): I dug a little more into the issue, and it looks like the issue is specifically with `typeOf`, not, say, `typeRep`. Compare: {{{ $ /opt/ghc/head/bin/ghci GHCi, version 8.1.20160108: http://www.haskell.org/ghc/ :? for help λ> :set -XDataKinds λ> :m Data.Proxy Data.Functor.Compose Data.Typeable λ> typeRep (Proxy :: Proxy 'Compose) 'Compose λ> typeRep (Proxy :: Proxy 'Just) 'Just λ> typeRep (Proxy :: Proxy 'Proxy) 'Proxy }}} versus {{{ λ> typeOf (Proxy :: Proxy 'Compose) ghc: panic! (the 'impossible' happened) (GHC version 8.1.20160108 for x86_64-unknown-linux): piResultTy * TYPE 'Lifted * Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug λ> typeOf (Proxy :: Proxy 'Just) Proxy (TYPE 'Lifted -> Maybe (TYPE 'Lifted)) 'Just λ> typeOf (Proxy :: Proxy 'Proxy) Proxy (Proxy (TYPE 'Lifted) (TYPE 'Lifted)) 'Proxy }}} Those last two results definitely look funny. I'm guessing that the issue pertains to levity polymorphism. I'll try to see what I can find about how `typeOf` works. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11334#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler