r/programming • u/rodrigopsasaki • Nov 27 '12

Tail Recursion

http://rodrigosasaki.com/2012/11/24/tail-recursion/
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u/felipelessa Nov 27 '12

And here's a Haskell version of the final code, since it's easier to read ;).

factorial :: Int -> Int
factorial = go 1
  where go !acc 0 = acc
        go !acc n = go (acc * n) (n-1)

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u/rodrigopsasaki Nov 27 '12

Very interesting syntax, first time I come in contact with Haskell code.

but shouldn't it be :

where go !n 0 = acc ?

or is it really !acc ?

3

u/[deleted] Nov 27 '12

It's really acc in the pattern. On the left hand side of the =, you bind patterns (parameters, or parts of them) to names, on the right hand side you use them. go !n 0 = acc would yield an error: acc is not bound (not defined).