#8171: Extending ExtendedDefaultRules -------------------------------------+------------------------------------ Reporter: ekmett | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by simonpj): The extended-default rules for a bunch of constraints (C1 a1, C2 a2, ...) are these: 1. The type variable a appears in no other constraints 2. All of the classes Ci are single-parameter type classes. 3. At least one of the classes Ci is numeric, or is Show, Eq, or Ord. We could, I suppose, relax it by simply abolishing Rule 3. That would certainly solve your problem, and would require little engineering effort. I don't know what the unintended consequences might be. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8171#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler