Accessed and updated functions in External Functions

The more complicated case is given when an asm B being used as an external function in A accesses and updates functions declared in A. Due to the fact that A doesn't make any step during the run of B, rules in B updating dynamic functions declared in A are actually not performed from B's point of view. Therefore, in XASM the semantics of updated functions in external asm functions is defined in a way, that these kind of unintuitive behavior is avoided:

• For each function f being marked as ``updated'' a local function with the same name is (internally) declared in B;
• this local function is initialized with the values of the original function in A;
• during the run of B, the functions marked as ``updated'' can be accessed like any other local function in B;
• on termination of B the updated locations of these function are propagated to the original function declared in the parent asm A.

This ensures, that all updates of an ``updates'' function are accessible in B, and that only the last updates are forwarded to the parent A. In general, the updates of functions declared in A and updated in B are treated as being part of the update set of A's current step. As a consequence, multiple invocations of B in the same step of A do not influence each other.

Consider the following - somewhat artificial - example:

In each step of the run of asm B the value of the updated function f(0) is updated with a new value. The semantics of the ``updates'' declaration in XASM ensures that all updates of f are accessible in B and that only the last update of f in B is propagated to the parent asm A. In this example, the update f(0) := 2 is propagated to A, while all other updates occurring in the ``internal'' steps in B have only local effects in B.