Question

I have defined a module in a file mod.ml as follows:

module Area = struct
  ...
  let test : unit =
    Print.printf "haha"
  ...
end;;

Print.printf "hehe";;

Area.test

It seems that without ;; after end, I can not compile the code by ocamlc. But it looks strange to me to have ;; in a Ocaml file, do I have to keep them?

After generating mod by ocamlc, I launch mod, it prints hahahehe. It seems that haha is printed by the definition of let test : unit ... instead of its call Area.test. What I except as a result is hehehaha or hahahehehaha. Could anyone explain why it is not what I expected?

Answer 1

I never use ;; in my source files, I think of it as part of the top-level interface. For your code I would probably write:

module Area = struct
  let test : unit -> unit =
      fun () -> Printf.printf "haha"
end

let () =
    Printf.printf "hehe";
    Area.test ()

For what it’s worth, Area.test as you have defined it is not a function, it’s just a unit value with a side effect during its computation. In my code here I’ve changed it to a function of type unit -> unit.