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?