30 Dec
2009
30 Dec
'09
5:35 p.m.
As an aside, in one of my libraries I have a combinator for folding a list in a binary-subdivision scheme.
foldm :: (a -> a -> a) -> a -> [a] -> a foldm (*) e x | null x = e | otherwise = fst (rec (length x) x) where rec 1 (a : as) = (a, as) rec n as = (a1 * a2, as2) where m = n `div` 2 (a1, as1) = rec (n - m) as (a2, as2) = rec m as1
Then factorial can be defined more succinctly
factorial n = foldm (*) 1 [1 .. n]
Cheers, Ralf