(* The map function: *)

let ls = [ 1.0; 2.0; 3.0; 4.0; 5.0; 6.0 ]

let comb2_map f ls =
  let rec aux ls acc =
    match ls with
    | [] -> (List.rev acc)
    | x::xs ->
        let x, ys =
          List.fold_left (fun (x, ys) y ->
            let x, y = (f x y) in
            (x, y::ys)
          ) (x, []) xs
        in
        aux (List.rev ys) (x::acc)
  in
  aux ls []

let () =
  let fs =
    comb2_map (fun v1 v2 ->
      match (v1, v2) with
      | (5.0, 4.0) | (4.0, 5.0) -> (4.0 -. 0.2, 5.0 +. 0.2)
      | orig -> orig
    ) ls
  in
  List.iter (fun (v) ->
    Printf.printf " (%g)\n" v
  ) fs

(*
Reslut:
*)

(*
 (1)
 (2)
 (3)
 (3.8)
 (5.2)
 (6)
*)