Write a function splitList that gives all the ways to split a list of at least two elements in two non-empty parts. The type declaration is:

  splitList :: [a] -> [([a],[a])]

The call splitList [1..4] should give:

  [([1],[2,3,4]),([1,2],[3,4]),([1,2,3],[4])]

Solution 1 - using a result list:

splitList :: [a] -> [([a],[a])]
splitList xs | length xs < 2 = error "Input list must have at least 2 elements"
splitList (x:xs) = splitList' [] [x] xs where
  splitList' :: [([a],[a])] -> [a] -> [a] -> [([a],[a])]
  splitList' rs xs [] = rs -- rs holds the result
  splitList' rs xs (y:ys) = splitList' (rs++[(xs,y:ys)]) (xs++[y]) ys

Solution 2 - without a result list:

splitList2 :: [a] -> [([a],[a])]
splitList2 [x,y] = [([x],[y])]
splitList2 (x:y:ys) = ([x],(y:ys)) : splitList2' [x,y] ys where
  splitList2' :: [a] -> [a] -> [([a],[a])]
  splitList2' xs [] = []
  splitList2' xs (y:ys) = (xs, (y:ys)) : splitList2' (xs++[y]) ys