SIMSCRIPT II.5 Programming Language

SIMSCRIPT II.5 Programming Language
arguments are transmitted and received is clear: at entry to the routine, the given value of X is used
to initialize the local argument NUMBER; at return from the subprogram, the named variable, in this
case X, is replaced by the resulting yielded argument, SQRT. Note that the same names may be used
in both the call statement and the routine definition, as in the fourth example above. In the call
statement, the given and yielding arguments refer either to variables local to the routine or to global
variables. In the routine, however, these arguments are always taken as definitions of variables local
to the routine, and thus, within the routine, do not directly reference the variables appearing in
the call statement.
It is important to note that the variables listed as given or yielded arguments in a routine reference
must match exactly, in number and mode, the arguments listed in the formal argument list in the
routine definition. No automatic mode conversions, between integer and real, for example,
may be assumed. Obviously, all references to a subprogram in different places in a program should
include the same numbers of both given and yielding arguments. In order that any incorrect references
may be diagnosed at program compilation, it is possible to define, in the program preamble,
the "correct" numbers of arguments, using a statement of the form:
define name as a routine given i arguments yielding j arguments
More than one routine may be defined in the same statement; a is optional, and the word routines
may be used. The word values is synonymous with arguments, and with and giving with
given. Either or both of the given or yielding phrases may be omitted. If either is omitted the
routine is assumed to have no such arguments. If neither given nor yielding phrases are included,
compilation checks on argument numbers at each routine reference are omitted. Otherwise,
inconsistent argument numbers will result in error messages. Some implementations provide for
additional checks during program execution. Consult the relevant user's guide for options on such
checking.
2.13 Routines Used as Functions
A function is a procedure that yields a single result value when applied to some given value. The
value yielded is termed the result of the function, or the function value. Calculation of the square
root of a given number could be considered to be a function evaluation, and a routine may be written
to provide this service. The call statement, however, is a cumbersome way of referencing routines,
which return only a single result value.
When a function is used in a mathematical expression, it indicates that the value that results from
applying the function to the appropriate given values should be used in evaluating the expression.
In programming, a function notation provides a convenient way to reference a subprogram that returns
only a single result value. A subprogram that is to be referenced as a function is written in
much the same way as subprograms discussed previously, requiring only minor changes in definition.
The function symbol is the name of the function routine. If the routine SQUARE.ROOT were
defined as a function, it could be referenced with a direct use of the name; as follows:
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