Re: [Haskell-cafe] Differences in optimisiation with interactive andcompiled mo

From: Daniel Fischer To: Bulat Ziganshin CC: Haskell-Cafe@haskell.org Subject: Re: [Haskell-cafe] Differences in optimisiation with interactive andcompiled mo Date: Sun, 11 Dec 2005 14:59:55 +0100

Am Samstag, 10. Dezember 2005 22:42 schrieb Bulat Ziganshin:

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Hello Branimir,

Saturday, December 10, 2005, 8:29:09 PM, you wrote:

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Can you check this version?

and this:

replace from to = repl where repl s | Just remainder <- start_from from s = to ++ repl remainder repl (c:cs) = c : repl cs repl [] = []

start_from (x:xs) (y:ys) | x==y = start_from xs ys start_from [] str = Just str start_from _ _ = Nothing

This is the fastest, even without type signatures (those give a wee bit of extra speed).

your test (unlikely in real scenario): $ time replace1 Working very long False Done real 0m12.531s user 0m0.015s sys 0m0.000s my test is not any more 0.25 secs with your test, becasue I've sacrifised that for my test speed :) bmaxa@MAXA ~/tutorial $ time searchr Working very long True Done real 0m4.000s user 0m0.031s sys 0m0.000s my test: bmaxa@MAXA ~/tutorial $ ghc -fglasgow-exts -O2 replace1.hs --make -o replace1.exe Chasing modules from: replace1.hs Compiling Main ( replace1.hs, replace1.o ) Linking ... bmaxa@MAXA ~/tutorial $ ghc -fglasgow-exts -O2 searchr.hs --make -o searchr.exe Chasing modules from: searchr.hs Compiling Main ( searchr.hs, searchr.o ) Linking ... bmaxa@MAXA ~/tutorial $ time replace1 Working:seasearch replace able seaseasearch baker seasearch charlie True Done real 0m11.718s user 0m0.015s sys 0m0.015s bmaxa@MAXA ~/tutorial $ time searchr.exe Working:seasearch replace able seaseasearch baker seasearch charlie True Done real 0m13.921s user 0m0.015s sys 0m0.015s

Have you any idea why using a pattern guard is faster (not much, but consistently) than the equivalent case-expression?

Probably because either then function is better inlined, or there is optimised tail recursion. In any way ghc very well optimises recursion. I didn't notice any difference in speed whether function signature is tagged only for strings or is polymorphic. So we can freely make polymorphic signatures. Greetings, Bane. _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/