Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!sunic!draken!jmr
From: jmr@nada.kth.se (Jan Michael Rynning)
Newsgroups: comp.lang.postscript
Subject: Re: PostScript question (help needed)
Message-ID: <2600@draken.nada.kth.se>
Date: 21 Dec 89 07:42:17 GMT
References: <314@vidiot.UUCP> <129367@sun.Eng.Sun.COM> <342@vidiot.UUCP>
Reply-To: jmr@nada.kth.se (Jan Michael Rynning)
Organization: Royal Institute of Technology, Stockholm, Sweden
Lines: 36

In article <342@vidiot.UUCP> brown@vidiot.UUCP (Vidiot) writes:
>I have looked at that read book, but never got the info described from it.
>Adobe also used the word popped when describing taking the currently dictionary
>off the stack.  OK, every microcomputer chip that I have programmed loses any
>data that is popped off of a stack, unles you move it somewhere else.  I can't
>find in the red book where it says that when the current dictionary is popped
>of the stack it is actually saved somewhere (like VM). 

A directory is a composite object, just like a string or an array.  The
PostScript interpreter will never push a composite object on any stack,
only a pointer to it.  So, when you do

  20 dictionary

the interpreter creates a dictionary which can hold up to 20 entries, and
pushes a pointer to that dictionary on the operand stack.  Then, when you
do

  begin

the interpreter pops that pointer from the operand stack and pushes it on
the dictionary stack.  Finally, when you do

  end

the interpreter pops the pointer from the dictionary stack and throws it
away.  It does not destroy the dictionary that the pointer points to, so
if you have saved away a copy of the pointer in some other place, you can
still access that dictionary.

Jan Michael Rynning,			jmr@nada.kth.se
Department of Numerical Analysis	If you can't fully handle domains:
  and Computing Science,		ARPA: jmr%nada.kth.se@uunet.uu.net
Royal Institute of Technology,		UUCP: {uunet,mcvax,...}!nada.kth.se!jmr
S-100 44 Stockholm,			BITNET: jmr@sekth
Sweden.					Phone: +46-8-7906288