Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!linus!philabs!prls!pyramid!decwrl!amdcad!tim
From: tim@amdcad.UUCP (Tim Olson)
Newsgroups: net.lang.forth
Subject: Information Hiding in FORTH
Message-ID: <12110@amdcad.UUCP>
Date: Wed, 25-Jun-86 12:35:47 EDT
Article-I.D.: amdcad.12110
Posted: Wed Jun 25 12:35:47 1986
Date-Received: Fri, 27-Jun-86 05:37:56 EDT
Organization: AMDCAD, Sunnyvale, CA
Lines: 45

I have been recently thinking of a way to implement something like the
'C' static scoping type in forth.  This would allow a word or group of
words to use a VARIABLE without letting the VARIABLE be visible outside
the group; something like:

	: random-package ;
	
	VARIABLE randval
	
	: init-rand ( seed -- )
		randval ! ;
	
	: rand ( range -- rand# )
		randval @ 21709 + 15273 * randval !
		mod ;
	
	HIDE randval

(No flames on the "randomness" of this random package, please :-)

HIDE is a word which, like tic ('), searches the dictionary for the
target word.  HIDE also keeps a trailing pointer to the previous
word in the dictionary.  When it finds the target word in the dictionary,
it takes it out of the dictionary search path by changing the previous
word's next pointer to point to the word following the target word.
This allows a VARIABLE or procedure word to be used normally in a
"package" and then be hidden from subsequent definitions.

	a)  Is this a useful construct, or is it the attempt of an
	    admittedly neophyte forth programmer (me) to force
	    other language ideas onto forth?

	b)  Can HIDE be written in forth, or must it be written in
	    assembly language?

	c)  Is there another (easier) way to do this that I am not
	    aware of?

	Tim Olson
	Advanced Micro Devices
	ihnp4!amdcad!tim

no.6: "What do you want?"
no.2: "Information."
no.6: "You won't get it!"