Ocaml Review Coding

Code can be found here: https://raw.github.com/louis1204/ocaml_training/master/pa1review.ml

(* returns the sum of a list *)
let rec sumList list = match list with
[] -> 0
| head::tail -> head + sumList tail;;

Pretty straight forward.



(* returns the digits of an int *)
let rec digitsOfInt num = 
if num < 10
    then [num]
else
  digitsOfInt(num/10) @ [num mod 10];;

This was also pretty straight forward. A refresher to me was the use of @ to concat two lists.



(* additive persistence. # of sums of digits until 1 digit *)
let additivePersistence num = 
  let count = 0 in
    let rec breakdown(n, counter) = 
      if n > 9 then
   breakdown(sumList(digitsOfInt(n)), (counter+1))
      else
   counter
    in
    breakdown(num, count);;

This was a bit challenger and I had to look at my previous answer. I was having trouble coming with a solution to have a counter. 
In the end we define a count in the scope of additivePersistence to handle the counting, then the recursive function, breakdown
to continually breakdown the number.



(* digital root. the resulting number from additive persistence *)
let digitalRoot num = 
  let count = 0 in
    let rec breakdown(n, counter) = 
      if n > 9 then
   breakdown(sumList(digitsOfInt(n)), (counter+1))
      else
   n
    in
    breakdown(num, count);;


Pretty much the same.

(* listReverse *)
let rec listReverse list = match list with
[] -> []
| head::tail -> listReverse(tail)@[head];;

(*explode*)
let explode s = 
  let rec _exp i = 
    if i >= String.length s then [] else (s.[i])::(_exp (i+1)) in
  _exp 0;;

(*palindrome*)
let palindrome string = 
 if listReverse(explode(string)) = explode(string) then true
 else false;;