Tail-recursive merge sort in OCaml
- by CFP
Hello world!
I’m trying to implement a tail-recursive list-sorting function in OCaml, and I’ve come up with the following code:
let tailrec_merge_sort l =
let split l =
let rec _split source left right =
match source with
| [] -> (left, right)
| head :: tail -> _split tail right (head :: left)
in _split l [] []
in
let merge l1 l2 =
let rec _merge l1 l2 result =
match l1, l2 with
| [], [] -> result
| [], h :: t | h :: t, [] -> _merge [] t (h :: result)
| h1 :: t1, h2 :: t2 ->
if h1 < h2 then _merge t1 l2 (h1 :: result)
else _merge l1 t2 (h2 :: result)
in List.rev (_merge l1 l2 [])
in
let rec sort = function
| [] -> []
| [a] -> [a]
| list -> let left, right = split list in merge (sort left) (sort right)
in sort l
;;
Yet it seems that it is not actually tail-recursive, since I encounter a "Stack overflow during evaluation (looping recursion?)" error.
Could you please help me spot the non tail-recursive call in this code? I've searched quite a lot, without finding it. Cout it be the let binding in the sort function?
Thanks a lot,
CFP.
