#9693: Reloading GHCi with Template Haskell names can panic GHC -------------------------------------+------------------------------------- Reporter: maxs | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Template Haskell | Version: 7.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Still reproducible on HEAD, but you'll need a different `Fun.hs`: {{{#!hs module Fun where import Language.Haskell.TH stuff = do -- let x = mkName "X" x <- newName "X" sequence $ [dataD (return []) x [] Nothing [ normalC x [] ] []] }}} And you'll get a slightly different error message: {{{ λ> :r [1 of 2] Compiling Fun ( Fun.hs, interpreted ) [2 of 2] Compiling Main ( thbug.hs, interpreted ) ghc: panic! (the 'impossible' happened) (GHC version 8.1.20161010 for x86_64-unknown-linux): kcLookupTcTyCon APromotionErr RecDataConPE Call stack: CallStack (from HasCallStack): prettyCurrentCallStack, called at compiler/utils/Outputable.hs:1076:58 in ghc:Outputable callStackDoc, called at compiler/utils/Outputable.hs:1080:37 in ghc:Outputable pprPanic, called at compiler/typecheck/TcHsType.hs:1656:27 in ghc:TcHsType Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9693#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler