Given Exercise 14 from 99 Haskell Problems:
(*) Duplicate the elements of a list.
Eg.:
*Main> dupli''' [1..10]
[1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10]
I've implemented 4 solutions:
{-- my first attempt --}
dupli :: [a] -> [a]
dupli [] = []
dupli (x:xs) = replicate 2 x ++ dupli xs
{-- using concatMap and replicate --}
dupli' :: [a] -> [a]
dupli' xs = concatMap (replicate 2) xs
{-- usign foldl --}
dupli'' :: [a] -> [a]
dupli'' xs = foldl (\acc x -> acc ++ [x,x]) [] xs
{-- using foldl 2 --}
dupli''' :: [a] -> [a]
dupli''' xs = reverse $ foldl (\acc x -> x:x:acc) [] xs
Still, I don't know how to really measure performance .
So what's the recommended function (from the above list) in terms of performance .
Any suggestions ?
