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From: wmb@MITCH.ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: Re: redefining words
Message-ID: <9008070137.AA00402@ucbvax.Berkeley.EDU>
Date: 6 Aug 90 21:59:17 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: wmb%MITCH.ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
Organization: The Internet
Lines: 33

> I've got an application where the definitions of words may be changed
> many times, and I'd like the new definition to actually replace the
> old one rather than simply being tacked on for future use.  Is there
> any "standard" way to remove/replace words and reclaim the dictionary
> space for them?

No.  Some (not many) systems have this capability, but as far as I know
there is no "common practice" in this area (other than FORGETting back
to a certain point and reloading everything after that).

The most common scheme for replacing the definition of a word is called
"vectored execution", but it does not accomplish the aim of reclaiming
the dictionary space used by the old definition.

Vectored execution works as follows:

	VARIABLE 'FOO
	: FOO  'FOO @ EXECUTE  ;

To set the action performed by FOO , say to BAR , you execute

	' BAR FOO !

Some systems have a built-in mechanism for doing this, e.g.:

	DEFER FOO
	' BAR IS FOO

Another common technique is the DOER ... MAKE construct described in
_Thinking Forth_ .  Personally, I do not like DOER ... MAKE because it
adds yet another non-postfix syntactic construct to Forth.

Mitch