#9137: A way to match RULES only for literals ------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- In `GHC/Enum` we have {{{ {-# RULES "enumDeltaToInteger1" [0] forall c n x . enumDeltaToIntegerFB c n x 1 = up_fb c n x 1 #-} -- This rule ensures that in the common case (delta = 1), we do not do the check here, -- and also that we have the chance to inline up_fb, which would allow the constructor to be -- inlined and good things to happen. -- We do not do it for Int this way because hand-tuned code already exists, and -- the special case varies more from the general case, due to the issue of overflows. }}} This rule would be useful for all literals, not just for `1`. I remember a discussion that such a rule would be more useful if we had a way to specify that, for example (random syntax). {-# RULES "enumDeltaToInteger1" [0] forall c n x d . isLiteral d => enumDeltaToIntegerFB c n x d = up_fb c n x d #-} I’m reporting this now to be able to link to it from #9136, where this feature might also help. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9137 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler