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From: wmb@MITCH.ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: Bill's DOES
Message-ID: <9008101355.AA03188@ucbvax.Berkeley.EDU>
Date: 10 Aug 90 01:02:38 GMT
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Reply-To: wmb%MITCH.ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
Organization: The Internet
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> I'm curious, would someone mind posting a quick run-down of the
> alternate syntax for Does> to which Mitch alluded?

By way of introduction, this alternate syntax is often called
"Bill's DOES", because it was proposed by Bill Ragsdale, and it
is a pun on  <BUILDS ... DOES>  which was the old name for what
is now CREATE ... DOES>

The basic idea is that the "action clause" is defined *before* the
defining word.  The following discussion does not use Ragsdale's names
(because I am away from my library right now and can't look it us),
but does capture the spirit.

Instead of         : CONSTANT   CREATE ,   DOES> @   ;
You would write    (:)  @  ;    : CONSTANT  CREATE ,  <DOES  ;

The word (:) creates an anonymous colon definition.  The cfa of that
definition is left on the stack where it may be later used by <DOES ;

Note that in the new syntax, there is no longer a partial colon definition
(in this case " @ ; ") embedded inside another colon definition.  It turns
out that "Bill's DOES" is a whole lot easier to metacompile than DOES> .
Another nice property is that the syntax lends itself easily to multiple-
code-field words (defining words whose children have more than one action,
i.e. objects).

	START-ACTIONS
	(:) @ EXECUTE  ;
	(:) !  ;
	END-ACTIONS
	: DEFER  CREATE 0 ,  <DOES  ;

Mitch