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Juan Jose Garcia Ripoll wrote:
> Hi,
>
> can anybody point me to tutorials, papers, etc, on how to properly
> annotate strictness in Haskell code? I am concerned with the following
> stupid piece of code that eats a lot of memory and takes an incredible
> amount of time to produce some output. I hope somebody will help me in
> finding what I am doing wrong.
>
> Juanjo
>
> ---
> module Main where
>
> import Array
>
> produce :: Int -> Double -> Array Int Double
> produce n x = array (1,n) [(i,x) | i <- [1..n]]
>
> scprod :: Array Int Double -> Array Int Double -> Double
> scprod a b =
> case (bounds a, bounds b) of
> ((1,i), (1,j)) ->
> foldl (+) start [a!(x) * b!(x) | x <- [2..i]]
> where start = a!(1) * b!(1)
>
> main = print (show (scprod a a))
> where a = produce 1000000 1.0
>
> --
> Juan Jose Garcia Ripoll www: http://www.arrakis.es/~worm
> Univ. Castilla-La Mancha job: [EMAIL PROTECTED]
> ETSI. Industriales home: [EMAIL PROTECTED]
> Departamento de Matematicas
> c/Camilo Jose Cela, 3, Ciudad Real 13071 Spain
Using GHC and compiling with -O, if you write
scprod a b =sum' [a!x * b!x | x <- [1..snd (bounds a)]]
sum' :: Num a => [a] -> a
sum' [] = 0
sum' (x:xs) = x + sum' xs
you'll reduce the amount of memory needed, and also
the execution time, because GHC is able to detect that
sum' is strict.
If you use the predefined function sum instead of sum',
you'll obtain worse results (see attached figures, obtained
using the GHC heap profiler).
Best Regards,
Fernando
--
---------------------------------------------------
Fernando Rubio Diez
Dpto. Sistemas Inform�ticos y Programaci�n
Facultad de Ciencias Matem�ticas
Universidad Complutense. Madrid
mailto:[EMAIL PROTECTED]
http://dalila.sip.ucm.es/miembros/fernando
phone: (34) 91 394 4350 fax: (34) 91 394 4602
---------------------------------------------------
--Boundary_(ID_GV3PYkBrWKBkRhXtR3jVMw)
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<HTML>
Juan Jose Garcia Ripoll wrote:
<BLOCKQUOTE TYPE=CITE>Hi,
<P>can anybody point me to tutorials, papers, etc, on how to properly
<BR>annotate strictness in Haskell code? I am concerned with the following
<BR>stupid piece of code that eats a lot of memory and takes an incredible
<BR>amount of time to produce some output. I hope somebody will help me
in
<BR>finding what I am doing wrong.
<P> Juanjo
<P>---
<BR>module Main where
<P>import Array
<P>produce :: Int -> Double -> Array Int Double
<BR>produce n x = array (1,n) [(i,x) | i <- [1..n]]
<P>scprod :: Array Int Double -> Array Int Double -> Double
<BR>scprod a b =
<BR> case (bounds a, bounds b)
of
<BR> ((1,i), (1,j))
->
<BR>
foldl (+) start [a!(x) * b!(x) | x <- [2..i]]
<BR>
where start = a!(1) * b!(1)
<P>main = print (show (scprod a a))
<BR> where a = produce 1000000 1.0
<P>--
<BR>Juan Jose Garcia Ripoll
www: <A HREF="http://www.arrakis.es/~worm">http://www.arrakis.es/~worm</A>
<BR>Univ. Castilla-La Mancha
job: [EMAIL PROTECTED]
<BR>ETSI.
Industriales
home: [EMAIL PROTECTED]
<BR>Departamento de Matematicas
<BR>c/Camilo Jose Cela, 3, Ciudad Real 13071 Spain</BLOCKQUOTE>
<BR>Using GHC and compiling with -O, if you write
<P>scprod a b =sum' [a!x * b!x | x <- [1..snd (bounds a)]]
<P>sum' :: Num a => [a] -> a
<BR>sum' [] = 0
<BR>sum' (x:xs) = x + sum' xs
<P>you'll reduce the amount of memory needed, and also
<BR>the execution time, because GHC is able to detect that
<BR>sum' is strict.
<P>If you use the predefined function sum instead of sum',
<BR>you'll obtain worse results (see attached figures, obtained
<BR>using the GHC heap profiler).
<P>Best Regards,
<BR> Fernando
<PRE>--
---------------------------------------------------
Fernando Rubio Diez
Dpto. Sistemas Informáticos y Programación
Facultad de Ciencias Matemáticas
Universidad Complutense. Madrid
<A HREF="mailto:[EMAIL PROTECTED]">mailto:[EMAIL PROTECTED]</A>
<A
HREF="http://dalila.sip.ucm.es/miembros/fernando">http://dalila.sip.ucm.es/miembros/fernando</A>
phone: (34) 91 394 4350 fax: (34) 91 394 4602
---------------------------------------------------</PRE>
</HTML>
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