Is cleartomark good PS programming style?

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2 total messages Started by Rob Bradlee Mon, 10 Aug 1992 14:37

#1807

Author: Rob Bradlee
Date: Mon, 10 Aug 1992 14:37

31 lines
1269 bytes


Here is PostScript coding style question for all you gurus:  Let's say you
have a PS procedure that does some like this

/utility_procedure {
	mark
	%
	% imagine PS code here to do some useful things and load up the stack
	%
	% Now imagine some PS code that does a test based on some of the 
	% stack info to see if it's worth processing the rest of the data
	% on the stack
	{
	% test was true.  Process the rest of the items on the stack.
	}
	{
	% test failed. cleanup.
	cleartomark
	}  ifelse
} def


Is the cleartomark a legitimate way to make sure you've left the stack in good
shape or a cheap trick that absolves you from the effort of thinking?
Your opinions, please.
-- 
Rob Bradlee  w:(508)-658-5600 X5153 
Agfa Corporation.                      ...!{decvax}!cg-atla!bradlee
200 Ballardvale St.                        bradlee@cg-atla.agfa.com
Wilmington, Mass. 01887

Re: Is cleartomark good PS programming style?

#1842

Author: Jim DeLaHunt
Date: Fri, 21 Aug 1992 03:33

32 lines
1895 bytes

Rob Bradlee writes:

> Is the cleartomark a legitimate way to make sure you've left the 
> stack in good shape or a cheap trick that absolves you from the 
> effort of thinking?

The way I would phrase the question is: is it a legitimate and useful
technique to pass a variable number of parameters on the operand stack, 
delimited with a 'mark'?  In my opinion, yes, absolutely.  Sometimes
you really want a variable number of arguments, sometimes you really do
want to "throw out all remaining arguments", and mark ... cleartomark
provides a great way to do that.

Here's how I've used it:  my software reads feature invocation code from a
PPD (PostScript Printer Description) file.  I enclose the invocation code
in mark ... cleartomark and a stopped context, so that if my file goes to
a printer that doesn't support that feature, the feature invocation will
turn into a no-op.

For instance, here's how my software invokes letter-size paper:
	[ {
	statusdict /lettertray get exec
	} stopped cleartomark

Is it a cheap trick?  Well, any legitimate technique can also be used as
a cheap trick that absolves one from thinking.  "0 setlinewidth" comes to
mind.

	--Jim DeLaHunt, Developer Support, Adobe Systems Incorporated	
delahunt@adobe.com	...!{apple,decwrl}!adobe!delahunt      +1-415-962-3790
In programming style my word is law.  I work for Developer Support. :-)

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