Hí everybody,

Earlier today I was testing some code in ghci with ":set +s" enabled. For some reason I changed an if-then-else expressions to guards and I was surprised to find out that the memory usage declined significantly (around 20%).

Here is a function call output using if-then-else:

λ> inarow1 ls
1
(1.28 secs, 401,690,400 bytes)

And here is a function call output using guards:

λ> inarow1 ls
1
(1.18 secs, 313,690,576 bytes)

I ran both versions many times and this difference was consistent. Could you help me understand why?

Thanks

Miguel

P.S. I don't think it should matter but maybe it does, here is the function definition:

inarow1 :: forall a. Eq a => [a] -> Int
inarow1 []     = 0
inarow1 (x:[]) = 1
inarow1 ls     = aux 0 1 ls where
  aux :: Int -> Int -> [a] -> Int
  aux top curr (x:y:[])      = max top $ if x == y then curr + 1 else curr
  aux top curr (x:xs@(y:ys))
    | x == y    = aux top (curr + 1) xs
    | otherwise = aux (max top curr) 1 xs

And the list:

ls = [1..1000000]