• Simon Peyton Jones's avatar
    Fallout from more assiduous RULE warnings · a1dd7dd6
    Simon Peyton Jones authored
    GHC now warns if rules compete, so that it's not predicatable
    which will work and which will not. E.g.
    {-# RULES
      f (g x) = ...
      g True  = ...
    If we had (f (g True)) it's not clear which rule would fire.
    This showed up fraility in the libraries.
    * Suppress warnigns in Control.Arrow, Control.Category for class
      methods. At the moment we simply don't have a good way to write a
      RULE with a class method in the LHS.  See Trac #1595.  Arrow and
      Category attempt to do so; I have silenced the complaints with
      -fno-warn-inline-rule-shadowing, but it's not a great solution.
    * Adjust the NOINLINE pragma on 'GHC.Base.map' to account for the
      map/coerce rule
    * Adjust the rewrite rules in Enum, especially for the "literal 1"
      case.  See Note [Enum Integer rules for literal 1].
    * Suppress warnings for 'bytestring' e.g.
       libraries/bytestring/Data/ByteString.hs:895:1: warning:
          Rule "ByteString specialise break (x==)" may never fire
            because rule "Class op ==" for ‘==’ might fire first
          Probable fix: add phase [n] or [~n] to the competing rule
warnings.mk 4.57 KB