I've started a Wiki page, attached to GHC's collaborative documentation, as a place to collect advice about RULES. http://haskell.org/haskellwiki/GHC/Using_Rules Please feel free to elaborate it. Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users-bounces@haskell.org] | On Behalf Of Donald Bruce Stewart | Sent: 12 July 2006 01:41 | To: Malcolm Wallace | Cc: glasgow-haskell-users@haskell.org | Subject: Re: RULES pragmas | | Malcolm.Wallace: | > I have a question about {-# RULES #-} pragmas. Here is a very simple | > attempt to use them: | > | > module Simplest where | > {-# RULES | > "simplestRule" forall x. id (id x) = x | > #-} | > myDefn = id (id 42) | > | > I want to verify whether ghc-6.4.1 does actually fire this rule, but | > have so far been unable to do so. According to the manual (section | > 7.10.5), the flag -ddump-rules should list "simplestRule" if it has been | > parsed correctly, and -ddump-simpl-stats should list the number of times | > it has fired. But it does not appear in either listing. | > | > Reasoning that I have the syntax wrong, I have tried numerous variations | > on the indentation, added type signatures, etc., all to no avail. | > | > So what am I doing wrong? And is there any way to ask the compiler to | > give a warning if the RULES pragma contains errors? | | In this case, it's because it's missing -fglasgow-exts, I think. | The following works for me with both 6.4 and 6.5 compilers: | | module Simplest where | | {-# RULES | "simplestRule" forall x. id (id x) = x | #-} | | myDefn = id (id 42) | | when compiled with: | $ ghc-6.4.2 -fglasgow-exts -c -ddump-simpl-stats A.hs | | ==================== Grand total simplifier statistics | Total ticks: 11 | | 2 PreInlineUnconditionally | 3 PostInlineUnconditionally | 1 UnfoldingDone | 1 RuleFired | 1 simplestRule | 4 BetaReduction | 2 SimplifierDone | | However, in general, you need to be careful that your identifiers | weren't inlined in the first phase. To control this we add an INLINE [1] | pragma to identifiers we want to match in rules, to ensure they haven't | disappeared by the time the rule matching comes around. | | Also, you need -O to have rules kick in locally. | | So, | module Simplest where | | {-# RULES | "simplestRule" forall x. myid (myid x) = x | #-} | | myDefn = myid (myid 42) | | myid x = x | {-# INLINE [1] myid #-} | | And: | $ ghc-6.4.2 -fglasgow-exts -O -c -ddump-simpl-stats A.hs | | ==================== Grand total simplifier statistics ==================== | Total ticks: 15 | | 6 PreInlineUnconditionally | 2 UnfoldingDone | 1 RuleFired | 1 simplestRule | 5 BetaReduction | 1 KnownBranch | 8 SimplifierDone | | Cheers, | Don | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users