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From: greid@adobe.com (Glenn Reid)
Newsgroups: comp.lang.postscript
Subject: commenting out blocks of code
Message-ID: <1100@adobe.UUCP>
Date: 23 Aug 89 21:49:45 GMT
Sender: news@adobe.COM
Reply-To: greid@adobe.COM ()
Organization: Adobe Systems Incorporated, Mountain View
Lines: 54

I've been writing serious PostScript code for over 4 years
and I just thought of this.  I wonder what that means....

There is only one comment mechanism in PostScript, which
is the % character.  It comments through the end of the
line.  So, to comment out a block of code, you do
something like this:

% /F { %def
%     findfont
%     exch scalefont
%     setfont
% } bind def

In fact, I've written an emacs macro to do this very
thing, and also to delete them as necessary.

Yesterday it dawned on me that there is another mechanism
for effectively commenting out blocks of code that is a
lot easier.  It doesn't really comment out the code, but
it keeps it from executing, which amounts to the same thing,
since you typically only do it while you're debugging:

{	% <--------- add this line
 /F { %def
    findfont
    exch scalefont
    setfont
 } bind def
} pop 	% <--------- also this line

It's only two lines, regardless of the number of lines in
between (assuming you don't overflow the operand stack,
that is).  Reminiscent of Pascal comments, methinks.

Since procedure bodies are always constructed as arrays
with deferred execution, you just force the code into a
procedure then pop it from the stack.  It works with
essentially all PostScript constructs in between, with
the exception of mismatched (), <>, or {} delimiters
and perhaps something else.

Since { is easy to miss, I now use something a little more
noticeable, like this:

{ %%%%%%%%%%%

} pop %%%%%%%

Just thought I would pass this on.  I suppose the rest
of you have been using this technique for years :-)

Glenn Reid
Adobe Systems