Cesar Augusto Acosta Minoli wrote:
Hello! I'm Working with Lists in Haskell, I´m a Beginner in Functional Programming and I would like to know if there is a way to write a more efficient function that return the length of a list, I wrote this one:
long :: [a]->Int
long p = longitud p 0
where
longitud [] s=s
longitud (x:xs) s=longitud xs (s+1)
but I think that it have a lineal grow O(n).
Sure. The only way to count the elements in a list is to, well, count the elements; it's an inherently linear operation.
One suggestion, though is that you're working too hard; there's really no reason to define a locally defined function. The much simpler:
long [] = 0
long (x:xs) = 1 + long xs
will do quite nicely.
HTH,
--ag
thanks!
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