Re: [GHC] #10595: BuiltinRules override other rules in some cases.

#10595: BuiltinRules override other rules in some cases. -------------------------------------+------------------------------------- Reporter: gjsimms | Owner: Type: bug | Status: closed Priority: high | Milestone: Component: Compiler | Version: 7.11 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by Simon Peyton Jones ): In [changeset:"2d88a531b7e4dbf4016dca4b1ba3b5dc34256cf4/ghc" 2d88a531/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="2d88a531b7e4dbf4016dca4b1ba3b5dc34256cf4" Improve warnings for rules that might not fire Two main things here * Previously we only warned about the "head" function of the rule, but actually the warning applies to any free variable on the LHS. * We now warn not only when one of these free vars can inline, but also if it has an active RULE (c.f. Trac #10528) See Note [Rules and inlining/other rules] in Desugar This actually shows up quite a few warnings in the libraries, notably in Control.Arrow, where it correctly points out that rules like "compose/arr" forall f g . (arr f) . (arr g) = arr (f . g) might never fire, because the rule for 'arr' (dictionary selection) might fire first. I'm not really sure what to do here; there is some discussion in Trac #10595. A minor change is adding BasicTypes.pprRuleName to pretty-print RuleName. }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10595#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler