#8390: regression in handling of type variables in constraints on instances which do not appear in the instance head ----------------------------------------------+---------------------------- Reporter: aavogt | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects valid program | Unknown/Multiple Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by aavogt): While Compose may not be so interesting, the same thing prevents HList from having both a single class for polymorphic functions (Fun above) and having higher-order functions that work for some instances of that class (ones like F). Some faking can be done by having some associated types for Fun to calculate the argument from the result type etc. But that is uglier (see attached inf2). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8390#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler