recommendation for fortran code

[smoothdeveloper]

you can use bind(C) on function and subroutine definition.

also, when passing scalar values, you can annotate them with `value``

function add(a,b) bind(C) result(c)
  integer(kind=4), intent(in), value :: a,b
  integer(kind=4) :: c
  c = a + b
end function

value means the argument is passed by value, rather than pointer

this would be equivalent to

int32_t add(int32_t a, int32_t b);

I think this way you can skip most of the .h files, unless haskell relies on them.