On 01/11/05, Scherrer, Chad <[EMAIL PROTECTED]> wrote: > I was wondering... In my experience, it's worked much better to use > > sum' = foldl' (+) 0 > > than the built-in "sum" function, which leaks memory like crazy for > large input lists. I'm guessing the built-in definition is > > sum = foldr (+) 0 > > But as far as I know, (+) is always strict, so foldl' seems much more > natural to me. Is there a case where the build-in definition is > preferable? > > Chad Scherrer > Computational Mathematics Group > Pacific Northwest National Laboratory >
You don't always want (+) to be strict. Consider working with the ring of formal power series over, say, the integers. You don't want (+) to force the evaluation of an infinite formal summation which is passed to it, since that's an infinite loop, so it will have to be non-strict, somewhat like zipWith (+) over the lists of coefficients. - Cale _______________________________________________ Haskell mailing list [email protected] http://www.haskell.org/mailman/listinfo/haskell
