Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!ucsd!swrinde!cs.utexas.edu!uunet!pilchuck!amc-gw!thebes!mtk!marmar
From: marmar@mtk.UUCP (Mark Martino)
Newsgroups: comp.lang.forth
Subject: Forth/PostScript
Summary: Separated at birth?
Message-ID: <935@mtk.UUCP>
Date: 27 Nov 89 16:08:25 GMT
Reply-To: marmar@mtk.UUCP (Mark Martino)
Distribution: usa
Organization: Mannesmann Tally, Kent, WA 98032
Lines: 35

When I first looked at PostScript, I viewed it as Forth with some
elaborate graphic words.  I still believe one could do the same things
PostScript does by using Forth with graphic words, but I've discovered
quite a few differences between Forth and PostScript.

1)	In PostScript, all operands on the operand stack are eight bytes long.
	Some of them include a pointer to other data.
2)	There are sixteen data types in PostScript.
3)	Although  I haven't made much use of this feature, it is true that in
	PostScript one can use any of the sixteen data types as a key to find
	anything else in a dictionary.  I don't think you can do this in
	Forth, but like I said, I'm not sure how handy this is anyway.
4)	PostScript tags everything you create with a save level number.  It
	uses this number as a mechanism for memory allocation via the
	operators "save" and "restore".  The tag is part of the eight bytes
	in an operand.
5)	This next one may be implementation dependent, but the two
	interpreters I've looked at allow, even require, that you be able to
	call the interpreter recursively.
6)	A PostScript interpreter takes over 300 Kbytes of compiled code.  And
	I have to differ with conventional wisdom here.  The amount of code
	is NOT just because of "a rich set of graphic operators".  Forth
	could draw the same lines and paint the same pictures for a lot less
	code.  What takes up the space in PostScript is the data structures
	it uses and the operators dedicated to handling these structures.
	Also, except for one implemenation in Forth, PostScript is written in
	C and a little assembly language. 
7)	A large part of PostScript is aimed at creating lovely fonts and it
	does this very well.

One other thing, PostScript was intended to generate images in a way
that would reduce the amount of transmitted data.  Although Forth started
out controlling telescopes, it has a more general purpose than
PostScript.
general charter than that