> > 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 (,) _______________________________________________ Haskell mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell
