#13659: Bug report: "AThing evaluated unexpectedly tcTyVar a_alF" -------------------------------------+------------------------------------- Reporter: costaparas | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Compile-time | (amd64) performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Description changed by costaparas: @@ -24,1 +24,1 @@ - a.hs:12:27:ghc: panic! (the 'impossible' happened) + Printf.hs:12:27:ghc: panic! (the 'impossible' happened) New description: The following code: {{{#!hs {-# LANGUAGE GADTs, EmptyDataDecls, TypeFamilies, TypeOperators, DataKinds, FlexibleInstances #-} {- Defines a C-like printf function using DataKinds extensions. -} module Printf where -- format string parameterized by a list of types data Format (fmt :: [*]) where X :: Format '[] -- empty string, i.e. "" L :: a -> String -> Format '[] -- string literal, e.g. "hello" S :: a -> Format '[String] -- "%s" I :: Format a -> Format '[Int, a] -- "%d" }}} produces the following error: GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Printf ( Printf.hs, interpreted ) Printf.hs:12:27:ghc: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-linux): AThing evaluated unexpectedly tcTyVar a_alF Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug when run using **ghci Printf.hs** on Liunx Ubuntu 16.04 LTS 64-bit with Intel® Core™ i7-7500U CPU @ 2.70GHz -- -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13659#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler