From: Daniel Fischer <[EMAIL PROTECTED]>
To: Bulat Ziganshin <[EMAIL PROTECTED]>
CC: [email protected]
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:
> Hello Branimir,
>
> Saturday, December 10, 2005, 8:29:09 PM, you wrote:
> >>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 :)
[EMAIL PROTECTED] ~/tutorial
$ time searchr
Working very long
True
Done
real 0m4.000s
user 0m0.031s
sys 0m0.000s
my test:
[EMAIL PROTECTED] ~/tutorial
$ ghc -fglasgow-exts -O2 replace1.hs --make -o replace1.exe
Chasing modules from: replace1.hs
Compiling Main ( replace1.hs, replace1.o )
Linking ...
[EMAIL PROTECTED] ~/tutorial
$ ghc -fglasgow-exts -O2 searchr.hs --make -o searchr.exe
Chasing modules from: searchr.hs
Compiling Main ( searchr.hs, searchr.o )
Linking ...
[EMAIL PROTECTED] ~/tutorial
$ time replace1
Working:seasearch replace able seaseasearch baker seasearch charlie
True
Done
real 0m11.718s
user 0m0.015s
sys 0m0.015s
[EMAIL PROTECTED] ~/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.
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