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From: ralphm@elaine19.stanford.edu (Ralph Melton)
Newsgroups: comp.sys.mac.programmer
Subject: Variable procedures in Pascal
Message-ID: <1990Nov23.082345.12074@portia.Stanford.EDU>
Date: 23 Nov 90 08:23:45 GMT
Sender: news@portia.Stanford.EDU (USENET News System)
Organization: Stanford University - AIR
Lines: 44

I am using Think Pascal 3.01, and I really want to be able to declare
procedural variables.  I am writing a code resource for that calls one
procedure from another procedure many, many times.  However, the behavior
of this procedure depends on whether Color Quickdraw is available.
Currently, this looks like this:

{A1 is the procedure executed with ColorQD; A2 is the one executed without
ColorQD}

Procedure A;
begin
  if Color_QuickDraw_Is_Available then
    do A1
  else do A2
end;

Procedure B;
begin
  {lots of calls to procedure A}
end;

I would like to avoid repeating the check for Color Quickdraw by writing
something like this:

Procedure B;
var A : procedure;
begin
  if Color_QuickDraw_is_available then
    A := A1
  else A := A2;
  {lots of calls to procedure A, which is the correct one of the subprocedures}
end

I believe that it is possible to do such things in C, and I know about
procedural parameters in Pascal.  I also know that I can pass some Toolbox
routines the address of a procedure.  Is there any way to do what I want
within THINK Pascal?

Ralph
--
Ralph Melton	The White Rabbit	ralphm@portia.stanford.edu

"When you hear of a storybook romance, you don't think of the storybook
as being _Alice in Wonderland_ . . ."