TOPS-20 PASCAL Language Manual - Bitsavers

PROCEDURES AND FUNCTIONS
Data items declared in any particular block of a PASCAL program are
considered global to all its nested subprograms. Thus, d~ta items
declared in the main program block are global to alJ subprograms. A
subprogram can access its global identifiers. For example, the
function SYMMETRY above has no local variables. Tt uses the global
identifiers K and L, and the parameters A and Side, which are declared
in PRINT SYM ARRAY.
6.3 PARAMETERS
Subprograms communicate data with the main program and with each other
by means of parameters. A subprogram can have any number of
parameters, but need not have any at all.
The subprogram heading lists the forma] parameters, which specify the
type of data that will be passed to the subprogram. For example, the
formal parameter list for the procedure PRINT SYM ARRAY is the
following:
(VAR A ARR; Side: INTEGER)
This Jist specifies two parameters to be passed to PRINT SYM ARRAY:
the variable A of the previously defined type ARR, and the-~al~e Side
of type INTEGER.
Each formal parameter corresponds to an actual parameter, specified in
the subprogram call. For example, a valid procedure call to
PRINT_SYM_ARRAY is the following:
This procedure call passes the variable Current Arr and the value of
Current Side to PRINT SYM ARRAY.
The formal parameters are identifiers used in the subprogram; they
represent the actual parameters in each subprogram call. You can call
a subprogram several times with different actual parameters. At
execution, each formal parameter represents the variable or value of
the corresponding actual parameter. The formal-value parameters, and
the actual parameters to which they correspond, must be of identical
types.
6.3.1 Formal Parameters
The formal parameter list specifies the identifier for each parameter
and the type of each parameter to be used within the subprogram.
Format
( [mechanism specifier ]
[ [ mechanism specifier]
identifier list
identifier list
type;
type .•. ] );
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