SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
if STATUS.CODE = 1
or DIRECTION = 2
let STATUS = 0
Defining constants in this symbolic way greatly eases the task of program modification, should
some of these constant values have to be adjusted. Of course, variables could be assigned to these
constant values with similar effect. However, it is possible for variables to be inadvertently modified
with consequent effect on the meaning. In order to clearly distinguish constants defined in this
manner from program variables, it is suggested that a unique name construction be reserved for
those names that are to be substituted. The form used above, which does not detract from readability,
is to prefix all such names with a period.
Another potential use is in the redefinition of keywords in a program. For instance, the words procedure,
execute, and finish may be preferred to the SIMSCRIPT II.5 terms routine,
call, and end. Preceding a program with the statements:
define PROCEDURE to mean routine
define EXECUTE to mean call
define FINISH to mean end
allows the program to be written with this redefined vocabulary and then be translated into
SIMSCRIPT II.5 vocabulary before compilation.
The scope of the define to mean statement is similar to that of the normally statement. When
used in a program preamble, it extends throughout an entire program unless overridden. When used
in a routine, it holds (until overridden) for that routine only.
Entire sequences of statements can be generated directly into a program by an extended form of the
define to mean statement. The extended form allows more than one line of statements to be
substituted for a particular word, and it offers greater possibilities for macro-instruction generation.
The statement can be written in two ways:
and
substitute this line for word
substitute these i lines for word
In the first statement, the contents of the line following the statement are substituted for the word
wherever it appears. In the second statement, the contents of the following i lines are substituted.
As with the define to mean statement, totally blank cards and comments cannot be substituted.
Define to mean and substitute statements can be used freely in a program with few restrictions.
They can "call on" one another at different levels of substitution. The following statements
show how a series of define to mean and substitute statements can be applied to a program
statement and used to translate the words of the statement into legal SIMSCRIPT II.5 code.
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