Interleave List of Lists in Haskell

Question

I was wondering how could I write a function in Haskell that interleaves a list of lists into a single lists, for example, if I had a function called

interleav

Answer 1

we could do what you want

testList = [[1,2,3],[4,5,6],[7,8]]

interleave l = foldr' (concat [map (\x -> f x idx) l | idx <- [0..]])  
    where
        f x n = if (length(x)<=n) then Nothing else Just (x !! n)
        foldr' (x:xs) = case x of 
                         Nothing -> []
                         Just a  -> (:) a (foldr' xs)   

As required interleave [[1,2,3] [4,5,6] [7,8]] => [1, 4, 7, 2, 5, 8, 3, 6]