TOPS-20 PASCAL Language Manual - Bitsavers

PROCEDURES AND FUNCTIONS
6.3.1.3 Formal Procedure and Function Parameters - PASCAL allows
procedures and functions to be passed as parameters to other
procedures or functions. To do this, a full procedure or function
heading is given as one parameter of the procedure being declared.
For example, the following procedure declaration specifies one value
parameter and one function parameter:
F' f~ 0 C E D U I:~ E ACT U A L.
(V A l..! J NT E G E r~ ,
FUNCTION FORMAL.
(Fl:INTEGER):INTEGER);
VAL. := FORMAL (VAL + 1),
The formal function parameter takes one value integer parameter, and
returns an integer value. When procedure ACTUAL is called, you need
to supply it with two parameters: an integer value; and, the name of
a function which takes one integer argument and returns an integer
value. Note that ONLY the function name is passed to the procedure;
do NOT supply the function's parameters in the procedure call. They
are supplied when the procedure calls the function.
The parameter list of the formal procedure or function may consist of
anything that can be defined in a normal procedure or function
declaration, including value parameters, VAR parameters, conformant
arrays, and even other procedures and functions. These procedures and
functions obey the same rules as the formal procedure or function of
which they are a parameter.
The following is an example of a procedure heading with formal
procedures nest~d to two levels:
PROCEDURE OUTER(PROCEDURE FORMAL1(FUNCTION FORMAL2:REAL, B:REAL»,
Procedure OUTER has one parameter, a procedure. This procedure has
two parameters, a real-typed function (with no parameter.s) and a real
value parameter.
When a subprogram is called with a procedure or function parameter,
the parameter lists of the formal and actual parameters must be
congruous. This means that the parameter lists must have the same
number of parameters; and each corresponding parameter must be of the
same kind (value, VAR, etc.) and of the same type. In the following
example, procedure YOU BET could be passed as a parameter to procedure
OUTER above, because Y5U BET and FORMALl have congruous parameter
lists.
PROCEDURE YOU_BET(FUNCTION YOU:
REAL, BET: REAL),
In the following example, procedures PRINTHEX and PRINTOCTAL have
congruous parameter lists. Procedure PRINTBINARY's parameter list is
not congruous to either of the others because both of its parameters
are value parameters.
PROCEDURE PRINTHEX (VAL: INTEGER, VAR SIZE: INTEGER),
PROCEDURE PRINTOCTAL. (I: INTEGER, VAR F: INTEGER),
PROCEDURE PRINTBINARY (NUM:
INTEGER, WIDTH: INTEGER),
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