MODULE TCallback;
(* A top-level V3 procedure is C-callable after the callback ABI change. *)
FROM SYSTEM IMPORT ADDRESS, ADR;

PROCEDURE add (a, b : INTEGER) : INTEGER;
BEGIN
  RETURN a + b
END add;

PROCEDURE call_add (fn : ADDRESS; a, b : INTEGER) : INTEGER;
  EXTERNAL "m2_c_call_add";
PROCEDURE call_two (fn, a, b : ADDRESS); EXTERNAL "m2_c_call_two";

VAR
  ExitCode : INTEGER;
  gotA, gotB : ADDRESS;

PROCEDURE two (a, b : ADDRESS);
BEGIN
  gotA := a;
  gotB := b
END two;

BEGIN
  gotA := NIL;
  gotB := NIL;
  call_two(ADR(two), ADR(gotA), ADR(gotB));
  IF (call_add(ADR(add), 20, 22) = 42)
     AND (gotA = ADR(gotA)) AND (gotB = ADR(gotB)) THEN
    ExitCode := 42
  ELSE
    ExitCode := 1
  END
END TCallback.