DSO FFI

domath.sml

  fun naiveIsPrime n =
  let
    fun helper n agg =
      if agg = 1 then
        true
      else if n mod agg = 0 then
        false
      else
        helper n (agg - 1)
    in
      helper n (n-1)
    end



fun naivePrims n =
  let fun helper n x  =
    if n = 0 then
      []
    else if (naiveIsPrime x) then
      x::(helper (n-1) (x+1))
    else
      helper (n-1) (x+1)
  in
    helper n 2
  end



exception NoArgs

(*
val n = case CommandLine.arguments () of
  (x::nil) =>  Option.valOf (Int.fromString(x))
  | _ => raise NoArgs



val ns = naivePrims n
val _ = List.app  (print o (fn x => x ^ ",") o Int.toString) ns
*)

val e = _export "naiveIsPrime": (int -> bool) -> unit;
val _ = e naiveIsPrime

(* val driver = _import "driver" public: unit -> unit;
val _ = driver () *)

hello.c

#include <dlfcn.h>
#include <stdio.h>
#include <stdlib.h>


int main () {
  printf("hello world\n");
  void* lib_handle = dlopen("domath.dylib", RTLD_LOCAL|RTLD_LAZY);
  if (!lib_handle) {
    printf("[%s] Unable to load library: %s\n", __FILE__, dlerror());
    exit(EXIT_FAILURE);
  }

  printf("loaded handle\n");

  // bool (*naiveIsPrime)(int) = dlsym(lib_handle, "_naiveIsPrime");
  void (*domath_open)(void) = dlsym(lib_handle, "domath_open");
  if (!domath_open) {       // addRating is guaranteed to exist in libRatings.A.dylib
    printf("[%s] Unable to get symbol: %s\n", __FILE__, dlerror());
    exit(EXIT_FAILURE);
  }

  printf("loaded domath_open\n");
  printf("init sml runtime\n");
  domath_open();
  printf("done!\n");


  bool (*isPrime)(int) = dlsym(lib_handle, "naiveIsPrime");
  if (!isPrime) {       // addRating is guaranteed to exist in libRatings.A.dylib
    printf("[%s] Unable to get symbol: %s\n", __FILE__, dlerror());
    exit(EXIT_FAILURE);
  }

  printf("answer: %d\n", isPrime(4));


}

terminal

# -verbose 3 flag is ommited

$ ./build/bin/mlton -codegen llvm -default-ann 'allowFFI true' -link-opt -fPIC -format library domath.sml 
# on linux: relocation R_X86_64_32 against `CReturnP' can not be used when making a shared object; recompile with -fPIC
# on OSX: no problem 

$ gcc hello.c

$ ./a.out 
hello world
loaded handle
loaded domath_open
init sml runtime
zsh: segmentation fault  ./a.out