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

Simple recursive version:

inter :: [[a]] -> [a]
inter [] = []
inter xs = inter2 (filter (\x -> not (null x)) xs)
   where inter2 xs = map head xs ++ inter (map tail xs)

Now, about foldr...