#7974: Panic on a context with additional variable -------------------------------+-------------------------------------------- Reporter: monoidal | Owner: Type: bug | Status: new Priority: normal | Component: Compiler Version: 7.7 | Keywords: Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: Compile-time crash | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- File: {{{ {-# LANGUAGE GADTs #-} data X a where N :: (a ~ b) => X a k :: X a -> X b k N = N }}} Result with HEAD: {{{ X.hs:6:7: Couldn't match type ‛b’ with ‛b1’ ‛b’ is untouchable inside the constraints (a ~ b) bound by a pattern with constructor N :: forall a. a ~ b => X a, in an equation for ‛k’ at X.hs:6:3ghc: panic! (the 'impossible' happened) (GHC version 7.7.20130608 for x86_64-unknown-linux): No skolem info: b{tv ae1} [sk] Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} I got it by attempting to compile [http://hackage.haskell.org/package /data-category data-category] with HEAD. -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7974 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler