SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
If a set is to be ranked only by entry time of entities into it, a short form can be used. Depending
on whether the ranking gives highest priority to the earliest or latest arrival, the define statement
is written as:
or
define ARMY as a fifo set
define ARMY as a lifo set
If the first form is used, entities are stored on a first-in, first-out basis. If the second form is used,
entities are stored on a last-in, first-out basis.
All the statements described thus far assume that every set has a full complement of ownership and
membership attributes, that is, that both first and last, predecessor and successor pointers, and
counter and membership attributes are defined. To perform all of the available set manipulations,
they must all be present. When set needs are more modest, sets with fewer pointers can be designed
with a gain in efficiency.
In some cases, not all of the automatically defined set pointers are needed. This is true in FIFO- and
LIFO-defined sets, where entities are never inserted in the middle of a set, but only at the beginning
or end. A FIFO set need have only first, last, and successor pointers. A LIFO set need have only
first and successor pointers. FIFO and LIFO set organizations are shown in figure 4-20.
A clause can be appended to a set declaration statement to delete unused set attributes. Any or all
of the three owner-entity and three member-entity attributes may be deleted. If the first-in-set attribute
is deleted, the is empty logical expression cannot be used. If the membership attribute is
deleted, the is in set logical expression cannot be used. Table 4-2 below defines the statements
that cannot be used when certain set attributes are deleted.
The deletion clause is of the form:
without attribute list attributes
The attribute list consists of one or more of the letters F, L, P, S, N, and M. The presence of a
letter indicates that the attribute formed by prefixing it and a period to the set name is not automatically
generated. For example, the following statement defines a LIFO set:
define ARRIVALS as a LIFO set without L,P,N
and M attributes
Note that although it is possible to delete all attributes, doing so completely destroys the concept of
a set. The programmer is cautioned against deleting set attributes without carefully considering the
consequences.
When required, two or more sets having the same properties can be declared in the same define
statement. A list of set names can appear after the word define, and the word sets used instead
of set.
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