[SOLVED] How to make tail function return what I need?

How to make tail function return what I need?

I need to encode list in OCaml. Command: encode ['a','a','b','b','b','c'];; have to return [(2,'a');(3,'b');(1,'c')]

Now I have this function:

let encode list =
  let rec encodeHelper list acc = 
    match list with
    | [] -> []
    | head :: [] -> (1, head) :: []
    | head :: headNext :: tail -> 
        if head = headNext then 
          encodeHelper (headNext :: tail) (acc + 1)
        else 
          (acc, head) :: encodeHelper (headNext :: tail) acc
  in encodeHelper list 1
;;

But it returns:

: (int * (char * char * char * char * char * char)) list = [(1, ('a', 'a', 'b', 'b', 'b', 'c'))]

Solution

Your test data as shown at the top is not in the right form.

A list in OCaml has elements separated by semicolons (;). Your test data is using commas instead (,). Commas are used for tuples, which is why you're seeing a tuple in your result.

If you change , to ; in your test data you should see something closer to what you're looking for. There is at least one problem left to fix (in my testing).