Difference between revisions of "GHC/Using Rule"
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| − | == Using Rules in GHC == |
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| − | GHC's rewrite rules (invoked by the RULE pragma) offer a powerful way to optimise your program. This page is place for people who use rewrite rules to collect thoughts about how to use them. |
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| − | If you aren't already familiar with RULES, read this stuff first: |
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| − | * [http://www.haskell.org/ghc/docs/latest/html/users_guide/rewrite-rules.html The relevant section of the GHC user manual] |
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| − | * [http://research.microsoft.com/%7Esimonpj/Papers/rules.htm Playing by the rules: rewriting as a practical optimisation technique in GHC]. This paper, from the 2001 Haskell workshop, describes the idea of rewrite rules. |
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| − | === Advice about using rewrite rules === |
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| − | * Remember to use the flag <tt>-fglasgow-exts</tt> and the optimisation flag <tt>-O</tt> |
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| − | * Use the flag <tt>-ddump-simpl-stats</tt> to see how many rules actually fired. |
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| − | * You need to be careful that your identifiers aren't inlined before your RULES have a chance to fire. To control this we add an <tt>INLINE [1]</tt> pragma to identifiers we want to match in rules, to ensure they haven't disappeared by the time the rule matching comes around. |
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