OCaml - Compile OCaml and C code that uses Ctypes

Question

I'm trying to learn how to call routines in C directly from OCaml code, using the Ctypes library.

I have this basic example with two files: hello.ml and hello.c.

hello.ml looks like this:

open Ctypes
open Foreign

let hello = 
    foreign "hello" (float @ -> returning void)
;;

let () = 
    hello 3.15
;;

hello.c looks like this:

#include <stdio.h>

void hello(double x)
{
    if ( x > 0)
        printf("hello!\n");
}

How do I compile these two files into one executable?

The process of manually compiling/linking code is scary to me and I don't understand it very well. I usually use a Makefile template to compile my code because that's really easy.

Answer 1

Here's an example that I use on OS X.

in simple.c

int adder(int a, int b)
{
    return a + b;
}

and in simple.ml

open Ctypes
open Foreign
let adder_ = foreign
    "adder" (int @-> int @-> returning int)

let () =
  print_endline (string_of_int (adder_ 1 2))

Then I do

clang -shared simple.c -o simple.so 
ocamlfind ocamlopt -package ctypes.foreign -cclib simple.so -linkpkg simple.ml -o Test
./Test

And that should print out 3 on the terminal.