Procedure Pointers
From MidrangeWiki
Procedure pointers are a way to give a program a unique level of flexibility in the way logic is invoked.
Basically, it gives you the ability to store a procedure reference in a pointer variable ... and then invoke that procedure in your code.
The following is a basic example of how to use a procedure pointer:
// Possible procedures to call
D Addcust PR
D 5U 0 Value
D Updcust PR
D 5U 0 Value
D Delcust PR
D 5U 0 Value
// Prototype for generic procedure
D Process PR Extproc(Processptr)
D 5U 0 Value
// Pointer to hold procedure address
D Processptr S * Procptr
D Action S 1 Inz('A')
D Parameter S 5U 0
/Free
Select; // Assign appropriate procedure address to pointer
When Action = 'A';
Processptr = %Paddr(Addcust);
When Action = 'U';
Processptr = %Paddr(Updcust);
When Action = 'D';
Processptr = %Paddr(Delcust);
Endsl;
Process(Parameter); // Call appropriate procedure
/End-free
The prototype for each procedure must be consistent with the prototype associated with the procedure pointer; that is, they must accept the same parameters. But you can include the OPTIONS(*NOPASS) and/or OPTIONS(*OMIT) keywords to make some parameters optional or omissible.
(Copied from http://www.bmeyers.net/2005/09/using-callp-with-a-procedure-pointer.php)
