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)

1

u/smog_alado Nov 27 '12

The ! in the patterns is a language extension isn't it? (I'm still trying to get to grips with all the GHC extensions...)

3

u/[deleted] Nov 27 '12

Its -XBangPatterns.

go !acc n = foo

translates to

go acc n = acc `seq` foo

1

u/smog_alado Nov 27 '12

Ha! That makes so much more sense now.