Did you try strict +/-? In (,). I am just curious.
> -----Original Message-----
> From: Hal Daume III [mailto:[EMAIL PROTECTED]]
> Sent: Friday, February 08, 2002 3:53 PM
> To: Konst Sushenko
> Cc: Jorge Adriano; [EMAIL PROTECTED]
> Subject: RE: efficiency question
>
>
> I've tried using a strict fold:
>
> foldl' f a [] = a
> foldl' f a (x:xs) = (foldl' f $! f a x) xs
>
> but that has no effect (or minimal effect).
>
> --
> Hal Daume III
>
> "Computer science is no more about computers | [EMAIL PROTECTED]
> than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume
>
> On Fri, 8 Feb 2002, Konst Sushenko wrote:
>
> > >
> > > On Friday 08 February 2002 22:14, you wrote:
> > > > define
> > > >
> > > > test1 l =
> > > > let s1 = foldr (+) 1 l
> > > > s2 = foldr (-) 1 l
> > > > in (s1, s2)
> > > >
> > > > test2 l =
> > > > let s = foldr (\x (a,b) -> (x+a,x-b)) (1,1) l
> > > > in s
> > > >
> > > > why is test1 so much faster than test2 for long lists l (eg
> > > > [1..1000000])? replacing foldr with foldl makes it faster
> > > (of course),
> > > > but test2 is still much slower.
> > > >
> > > > i *expected* test2 to be much faster because you're only
> > > traversing the
> > > > list once. presumably the two elements "a" and "b" in
> > > test2 could be put
> > > > in registers and i'd imagine test2 should be faster (it
> > > certainly would be
> > > > if written in c).
> > >
> > > I'd say that's because in the second case you also got to
> > > apply the (,),
> > > besides the (+)/(-) constructor during the transversing...
> > > Am I right?
> > >
> > > J.A.
> >
> > My guess is that it is due to the laziness of the
> addition/subtraction
> > in (,)
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>
>
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