[Caml-list] Non-toplevel C functions using OCaml values

["Harrison, John R" <john.r.harrison@intel.com>]

I have a question about interfacing C and OCaml functions that I
didn't see an answer to in the manual, though maybe I just didn't look
carefully enough. I think I pretty well understand how to set up a C
function that is designed to be called directly by OCaml. But what
about a function that I want to use internally as a utility, callable
by other C functions that are themselves called by OCaml?

For example, if I want to implement a function designed to be called
directly by OCaml and basically equivalent to the OCaml definition

  let cons h t = h::t;;

then I think (correct me if I'm wrong) that I do the following:

  CAMLprim value caml_cons(value h,value t)
  { CAMLparam2(h,t);
    CAMLlocal1(newblock);
    newblock = caml_alloc(2,0);
    Store_field(newblock,0,h);
    Store_field(newblock,1,t);
    CAMLreturn(newblock);
  }

But what if I want to set up a utility that I'm only going to call
from other C functions, and which involves a mixture of standard C
types and OCaml values among its arguments or local variables, and/or
allocates OCaml values? For example, suppose I want to implement the
special case of the above "cons" for int lists where the first
argument is a C int (which I assume to be in range for an OCaml
int). I might guess that I would do something like this:

  value int_cons(int h,value t)
  { CAMLparam1(t);
    CAMLlocal1(newblock);
    newblock = caml_alloc(2,0);
    Store_field(newblock,0,Val_int(h));
    Store_field(newblock,1,t);
    CAMLreturn(newblock);
  }

and then just call it like any other C function. However, I can
imagine several other plausible alternatives, e.g. that I should skip
some or all of the special CAMLsomething functions, or that I should
just forget the idea and use OCaml values throughout, calling it as if
it were any other OCaml function. Can someone enlighten me?

John.