Which version of GHC are you using? GHC 6.10 implements automatically precisely the transformation you give below. If the difference shows up in GHC 6.10, could you spare a moment to produce a reproducible test case, and record it in GHC's bug tracker? Thanks Simon | -----Original Message----- | From: glasgow-haskell-users-bounces@haskell.org [mailto:glasgow-haskell-users- | bounces@haskell.org] On Behalf Of Dave Bayer | Sent: 28 December 2008 15:29 | To: glasgow-haskell-users@haskell.org | Subject: ghc -O2 and class dictionaries | | Using "ghc -O2" while tuning a class instance for performance, I | obtained a 13% speedup by applying the transformation | | > instance (Ord a, Num b) ⇒ Sum PSum a b where | > empty = empty | > insert = insert | > union = union | > unions = unions | > extractMin = extractMin | > fromList = fromList | > toList = toList | > map = map | > mapMaybe = mapMaybe | | and defining the instance functions outside the instance declaration, | rather than inside the instance declaration. | | Conceptually, I understand this as follows: After this transformation, | none of the recursive calls have to go through the class dictionary. | | Is this a transformation that ghc could automatically apply while | optimizing? It is clear at compile time that the recursive calls are | from this instance. Every 13% helps. | | (My example is adapting a pairing heap to sums of terms, e.g. to | define an algebra from a small category. So far, I can't beat | Data.Map, but I'm not done tuning. Other examples might not show the | same performance increase from this transformation.) | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users@haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users