Haskell Help

Okay, major help needed if someone out there has the time, this has been killing my brain for ages.

-- e.g., insertions 'c' "ab" = ["cab", "acb", "abc"]
-- It may help to define two functions which call each other.

Thus far I have.

insertions :: x -> [x] -> [[x]]
insertions x [] = [[]]
insertions x (y:ys) = ??

So, you want to insert 'c' into 'ab' at all possible positions, and return a list of those?


import Data.List (splitAt)

insertions :: a -> [a] -> [[a]]
insertions _ [] = []
insertions a as =
  let asrep = replicate (length as + 1) as
      zipped = zip [0..] asrep
      insert (n, l) = let (f, s) = splitAt n l in f ++ [a] ++ s
      inserted = map insert zipped
  in inserted