#8171: Extending ExtendedDefaultRules -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.3 Resolution: | Keywords: | ExtendedDefaultRules Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #2641 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by thomie): * keywords: => ExtendedDefaultRules * related: => #2641 Comment: Replying to [comment:5 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.
See also #2641 (still open), where you proposed to make these rules //less// liberal, albeit 7 years ago. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8171#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler