SIMSCRIPT II.5 Programming Language

Discrete Simulation Concepts
of events, before the event notice is destroyed, the values of the user-defined attributes are assigned,
in order, to these local argument variables. Only as many attributes as have corresponding argument
positions are copied. Specification of more arguments than there are user-defined attributes
has no meaning, and is not permitted. Care must be taken in selecting these argument names.
Should they be chosen as identical with the declared attribute names, then the local argument usage
will always take precedence, rendering subsequent access to the entity attributes themselves impossible.
This may be of significance in the process case, where the process notice must retain information
across the sequence of events within the process activity. The above event routine definition
could be written as:
event ARRIVAL given ORIGIN
where the now local argument ORIGIN will be initialized from the attribute value specified at the
time of scheduling.
Event notices that have not been destroyed may be reused, as in a case when the word this is required
in the scheduling statement, avoiding the creation of a new event notice entity. Care should
be taken, if this is done, that event notices be used only in appropriate event classes. It will become
apparent that this is the mechanism by which processes may represent more than one of the events
within an activity. The following examples demonstrate some of these points.
1. Accessing the attributes of a saved event notice. The event notice entity is saved for filing
in a user-defined set:
event DEPARTURE(NAME, DESTINATION) saving the event notice
let DEPARTURE.TIME(DEPARTURE) = time.v
add 1 to PASSENGER.LIST(DESTINATION(DEPARTURE))
file DEPARTURE in DEPARTURES.SET
return
end
2. Event notice reused to schedule another similar event. A separate entity is created for program-defined
manipulations:
event ARRIVAL given NAME, ORIGIN saving the event notice
define NAME, ORIGIN as text variables
create a JOB
let IDENTITY(JOB) = NAME
let PLACE(JOB) = LOCATION
file JOB in LIST.OF.JOBS
reschedule this ARRIVAL("WALDO", "ALASKA") in 5 days
return
end
3. A simple instantaneous process routine which behaves like an event. Note that the process
notice is not destroyed until exit from the routine and so the attribute IDENT may be accessed
from within the routine.
199