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Simon Peyton Jones authored
This patch adds an optional CONLIKE modifier to INLINE/NOINLINE pragmas, {-# NOINLINE CONLIKE [1] f #-} The effect is to allow applications of 'f' to be expanded in a potential rule match. Example {-# RULE "r/f" forall v. r (f v) = f (v+1) #-} Consider the term let x = f v in ..x...x...(r x)... Normally the (r x) would not match the rule, because GHC would be scared about duplicating the redex (f v). However the CONLIKE modifier says to treat 'f' like a constructor in this situation, and "look through" the unfolding for x. So (r x) fires, yielding (f (v+1)). The main changes are: - Syntax - The inlinePragInfo field of an IdInfo has a RuleMatchInfo component, which records whether or not the Id is CONLIKE. Of course, this needs to be serialised in interface files too. - The occurrence analyser (OccAnal) and simplifier (Simplify) treat CONLIKE thing like constructors, by ANF-ing them - New function coreUtils.exprIsExpandable is like exprIsCheap, but additionally spots applications of CONLIKE functions - A CoreUnfolding has a field that caches exprIsExpandable - The rule matcher consults this field. See Note [Expanding variables] in Rules.lhs. On the way I fixed a lurking variable bug in the way variables are expanded. See Note [Do not expand locally-bound variables] in Rule.lhs. I also did a bit of reformatting and refactoring in Rules.lhs, so the module has more lines changed than are really different.
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