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From: batcheldern@icosa.dec.com (Ned Batchelder)
Newsgroups: comp.lang.postscript
Subject: Re: The // operator
Message-ID: <2586@shlump.dec.com>
Date: 26 May 89 20:20:29 GMT
References: <441@mtk.UUCP>
Sender: news@shlump.dec.com
Distribution: usa
Organization: Digital Equipment Corporation
Lines: 20

The // construct in PostScript is not an operator; it is more like a name modifier. 
When a name is preceded by the double-slash, its current value is used instead of the

	/a 17 def
	/foo { a } def
	/bar { /a } def
	/baz { //a } def

"foo" is now a procedure which when executed will push the latest value of "a" on the
stack. The procedure actually contains the name "a", and it is looked up when the
procedure is executed.

"bar" is now a procedure which when executed will push the literal name "a" on the stack. No name lookup is performed.

"baz" is now a procedure which when executed will push 17 on the stack. The procedure actually contains the integer 17, because that is the value that "a" had at the time the procedure was defined. The double-slash means "lookup this name, and use its value just as it had appeared in the input". Of course, some values for names may not have a representation
in the input stream, such as dictionaries.

Be careful when using the double-slash (if at all), because older PostScript interpreters don't have it, and there is no way your program will work properly on them.

Ned Batchelder, Digital Equipment Corp., BatchelderN@Hannah.DEC.com