#12055: Typechecker panic instead of proper error -------------------------------------+------------------------------------- Reporter: bgamari | Owner: Type: bug | Status: new Priority: normal | Milestone: 8.0.2 Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: 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 simonpj): Well HEAD for this gives {{{ T12055.hs:18:1: error: • Non type-variable argument in the constraint: Category (Dom f) (Use FlexibleContexts to permit this) • In the context: (Category (Dom f), Category (Cod f)) While checking the super-classes of class ‘Functor’ In the class declaration for ‘Functor’ T12055.hs:26:1: error: • Fundeps in class ‘Fun’ (Use FunctionalDependencies to allow fundeps) • In the class declaration for ‘Fun’ T12055.hs:29:5: error: • Illegal instance declaration for ‘Fun p q f’ (All instance types must be of the form (T a1 ... an) where a1 ... an are *distinct type variables*, and each type variable appears at most once in the instance head. Use FlexibleInstances if you want to disable this.) • In the instance declaration for ‘Fun (p :: Cat j) (q :: Cat k) (f :: j -> k)’ }}} And if you add the missing language extensions {{{ {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} }}} then it compiles cleanly. I suppose someone could bisect their way to the patch that fixed HEAD. Or we could just leave it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12055#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler