Fri, 8 Feb 2002 22:50:40 +0000
On Friday 08 February 2002 22:14, you wrote:
> 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?