andrewcoppin:
Brandon S. Allbery KF8NH wrote:
On 2008 May 13, at 17:01, Andrew Coppin wrote:
That definition of mean is wrong because it traverses the list twice. (Curiosity: would traversing it twice in parallel work any better?) As for the folds - I always *always* mix up
Yes, using parallelism does work. It turns the naive definition into one which traverses the list on two cores at the same time, so the garbage collector does get clean up the list as each core races along it. mean ls = count `par` (total/count) where count = fromIntegral (length ls) total = foldl' (+) 0 ls It is kind of amazing how parallelism and laziness enable the naive definition to fall out as much the same as the explicitly recursive version. -- Don