One thing I hadn't seen really emphasized here is that modern functional languages such as Haskell really more on first class functions for flow control than explicit recursion. You don't need to define factorial recursively in Haskell, as was done above. I think something like
fac n = foldr (*) 1 [1..n]
is a perfectly idiomatic construction, and much closer in spirit to using a loop than to using explicit recursion.
