--mapMyList f Empty = Empty
--mapMyList f (x :-: xs) = f x :-: mapMyList f xs



tailRecursionEngine termCond termFn wayAheadFn =
  tailRecursiveFn
  where tailRecursiveFn y
           | termCond y = termFn y
           | otherwise = (tailRecursiveFn (wayAheadFn y))

--   :: (t1 -> Bool) -> (t1 -> t) -> (t1 -> t1) -> t1 -> t

data List a = Empty |  a :-: List a deriving (Read, Eq, Ord)

mapMyList1 :: (t -> a) -> List t -> List a

myNull Empty = True ; myNull (x :-: xs) = False

mapMyList1 f xs =
   tailRecursionEngine
   (myNull )   ---  termination Condition
   (\_  -> f(head :-: xs))
   (:-:)     --- Error message is in this line



Error Message


  Couldn't match expected type `List t'
           against inferred type `List (List t) -> List (List t)'
    In the third argument of `tailRecursionEngine', namely `(:-:)'
    In the expression:
        tailRecursionEngine (myNull) (\ _ -> f (head :-: xs)) (:-:)
    In the definition of `mapMyList1':
        mapMyList1 f xs
                     = tailRecursionEngine (myNull) (\ _ -> f (head :-: xs)) (:-:)