Haskell own function to merge two lists

Question

I need to write a function to merge two lists. Exactly like '++' is working.

let x = merge [1,2,3] [3,3,4] -- should output [1,2,3,3,3,4]

How should it be done?

Edit: solution is

merge :: [a] -> [a] -> [a]
merge []     ys = ys
merge (x:xs) ys = x : (merge xs ys)

@erthalion No, that's an unsorted interpolation. This merge sorts or concatenates, and I think they're asking for concatenation. — not my job, Jan 26 '14 at 09:01
erthalion, this is not what I am looking for as chunks said. — user3235761, Jan 26 '14 at 09:15

score 1 · Answer 1 · answered Jan 26 '14 at 09:17

Maybe something like this.

merge :: (a -> a -> Bool) -> [a] -> [a] -> [a]
merge pred xs []         = xs
merge pred [] ys         = ys
merge pred (x:xs) (y:ys) =
  case pred x y of
    True  -> x: merge pred xs (y:ys)
    False -> y: merge pred (x:xs) ys

(++) xs ys = merge (\x y -> compare x y == LT) xs ys

Or, if you just need to repeat the functionality of (++), you can look up it's definition with hoogle which eventually leads you to the source code

(++) []     ys = ys
(++) (x:xs) ys = x : xs ++ ys

Haskell own function to merge two lists

1 Answers1