Andrew Coppin
Look closer: it's hardER to read.
mean xs = sum xs / fromIntegral (length xs)
mean = go 0 0 n where go s l x | x > m = s / fromIntegra l | otherwise = go (s+x) (l+1) (x+1
One version makes it instantly clear, at a glance, what is happening. The other requires you to mentally walk round a look, imperative style, to figure out what's happening. It's not a *big* deal, but it's unfortunate.
I am new to Haskell and when I first saw the two versions side by side I too was disappointed with the second version. But after reading the great blog post by Don, I realized that the whole problem comes from the fact that lists in Haskell are not like arrays or vectors in other languages: you don't know how long they are before you have found the end. In other words: they behave like a linked lists -- lists that are generated lazily on demand. Because they are generated on demand you *cannot* really know the length beforehand, and thus you *must* traverse the list to its end to count the length. When the list is too big to fit in memory then it's clear that the code *must* let go of the beginning to allow the garbage collector to do its job. You wouldn't be able to work with a 7.5 GiB linked list otherwise. -- Martin Geisler VIFF (Virtual Ideal Functionality Framework) brings easy and efficient SMPC (Secure Multi-Party Computation) to Python. See: http://viff.dk/.