Indeed. I spent a year working rather intensively on both ML and Haskell (which are structurally similar but have some crucial differences) and one of the first things I learned is that while it's tempting to implement a factorial like this:

fact 0 = 1
fact 1 = 1
fact n | n < 0 = error "Negative factorial!"
       | otherwise = n * fact (n - 1)

[download]

your life will be vastly improved if you implement it like this:

fact 0 = 1
fact 1 = 1
fact n | n < 0 = error "Negative factorial!"
       | otherwise = g 1 n where
            g x 1 = x
            g x n' = g (x * n') (n' - 1)

[download]

because the latter uses tail recursion and the former doesn't.

In reply to Re^3: map: chaining vs. nesting by Errto
in thread map: chaining vs. nesting by Roy Johnson

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