#12072: GHC panic on type wildcard in left-hand side of data family -------------------------------------+------------------------------------- Reporter: andreash | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 Keywords: | Operating System: Linux Architecture: x86_64 | Type of failure: Compile-time (amd64) | crash Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- While playing around with data families I received the following output by ghc/ghci: {{{ ghc: panic! (the 'impossible' happened) (GHC version 7.10.3 for x86_64-unknown-linux): rnHsTyKi HsWildcardTy Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I had accidentally left a wildcard `_` on the left-hand side of a data instance definition. To reproduce enter the following code into a file and try to load that file into ghci, or try to compile it with ghc: {{{#!hs data family Bug x data instance Bug _ = Bug }}} The expected behavior would be a (non-panic) error message of some sort. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12072 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler