Re: desperately seeking RULES help

Thanks a million, Lennart! -fno-method-sharing was the missing piece. - Conal On Sat, Jun 7, 2008 at 5:07 AM, Lennart Augustsson wrote:

Here's something that actually works. You need to pass -fno-method-sharing on the command line. Instead of using rules on methods it uses rules on global functions, and these global functions don't get inlined until late (after the rule has fired).

-- Lennart

module F where

-- | Domain of a linear map. class AsInt a where toInt' :: a -> Int fromInt' :: Int -> a

{-# INLINE[1] toInt #-} toInt :: (AsInt a) => a -> Int toInt = toInt'

{-# INLINE[1] fromInt #-} fromInt :: (AsInt a) => Int -> a fromInt = fromInt'

{-# RULES "toInt/fromInt" forall m . toInt (fromInt m) = m #-}

{-# INLINE onInt #-} onInt :: AsInt a => (Int -> Int) -> (a -> a) onInt f x = fromInt (f (toInt x))

test :: AsInt a => (Int -> Int) -> (Int -> Int) -> (a -> a) test h g = onInt h . onInt g

...

I'm trying to do some fusion in ghc, and I'd greatly appreciate help with the code below (which is simplified from fusion on linear maps). I've

2008/6/7 Conal Elliott : tried

...

every variation I can think of, and always something prevents the fusion.

Help, please! Thanks, - Conal

{-# OPTIONS_GHC -O2 -Wall -fglasgow-exts -ddump-simpl -ddump-simpl-stats #-} -- {-# OPTIONS_GHC -ddump-simpl-iterations #-}

module F where

-- | Domain of a linear map. class AsInt a where toInt :: a -> Int fromInt :: Int -> a

{-# RULES "toInt/fromInt" forall m. toInt (fromInt m) = m #-}

{-# INLINE onInt #-} onInt :: AsInt a => (Int -> Int) -> (a -> a) onInt f = fromInt . f . toInt

test :: AsInt a => (Int -> Int) -> (Int -> Int) -> (a -> a) test h g = onInt h . onInt g

-- The desired result: -- -- test h g -- == onInt h . onInt g -- == (fromInt . h . toInt) . (fromInt . g . toInt) -- == \ a -> (fromInt . h . toInt) ((fromInt . g . toInt) a) -- == \ a -> (fromInt . h . toInt) (fromInt (g (toInt a))) -- == \ a -> fromInt (h (toInt (fromInt (g (toInt a))))) -- == \ a -> fromInt (h (g (toInt a)))

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