Re: [Haskell-cafe] Arrow preprocessor and *** combinator

On Thu, Apr 30, 2009 at 11:42 AM, Peter Verswyvelen wrote:

Thanks Ross. Does anyone know how to tackle this? Combining GHC's builtin arrow processor and rewrite rules?

Another possibility is to make an "optimizer" arrow transformer that encodes the rules. Eg. data Optimize a b c where Arr :: (b -> c) -> Optimize a b c (:>>>) :: Optimize a b c -> Optimize a c d -> Optimize a b d First :: Optimize a b c -> Optimize a (b,d) (c,d) Second :: Optimize a b c -> Optimize a (b,d) (c,d) (:***) :: Optimize a b b' -> Optimize a c c' -> Optimize a (b,b') (c,c') optimize :: Optimize a b c -> Optimize a b c optimize (First f :>>> Second g) = f :*** g ... compile :: (Arrow a) => Optimize a b c -> a b c compile (Arr f) = arr f compile (f :>>> g) = compile f >>> compile g ... I have of course handwaved over optimize, which will have some interesting traversal structure; esp. if you want to take advantage of the associativity of >>>. Unfortunately, Arr is not quite transparent enough to do everything one might want with this. e.g.,this rule cannot be encoded: swap (x,y) = (y,x) first f >>> arr swap >>> first g = f *** g >>> arr swap If you are serious about arrow optimizations, it might be worthwhile to modify the original preprocessor to output a richer GADT (with cases for things like ArrSwap) with all the information it knows, so that user code can experiment with optimizations. Godspeed on this interesting problem. Please publish :-) Luke

On Wed, Apr 29, 2009 at 3:43 PM, Ross Paterson wrote:

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After doing some pragmatic tests, it seems that neither the arrow

On Wed, Apr 29, 2009 at 03:07:25PM +0200, Peter Verswyvelen wrote: preprocessor

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nor GHC's builtin one generate / optimize to the (***) combinator.

Right, neither of them do that. It might be possible to do that using GHC rules, but it isn't done at the moment. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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