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From: john@aplcen.apl.jhu.edu (John Hayes)
Newsgroups: comp.lang.forth
Subject: Re: Compiling without :
Message-ID: <6533@aplcen.apl.jhu.edu>
Date: 12 Sep 90 13:39:18 GMT
Organization: Johns Hopkins University / Applied Physics Laboratory
Lines: 27


Andrew Scott writes on START:
> I like the word - I've used a similar construct many times before.  I have
> one question, though.  It's not stated in your description and example, but
> it is implied that ; cannot be used to end a code fragment started with
> START: .  You created ;sim in your example:
> 
> >     : ;sim   postpone exit postpone [ ; immediate
> 
> Am I correct in drawing this conclusion?

   There are two reasons why ; cannot be used with START:.  First, ; expects
a compile-time argument, a sys, to be present.  This sys is provided by
: (colon).  People who do syntax checking in their compilers use this
to pass a "magic cookie" from : to ; so that ; can check that it is
paired with a :.  START: could be specified to deliver this "magic cookie".
Since the size of a sys is implementation defined, the sys would have to be
beneath the execution token on the stack:
   START:      ( --- sys w )

   A second reason that ; cannot be used with : is that ; "makes the
most recent dictionary entry findable".  Since START: doen't make a header,
; unsmudges an earlier header.  This is probably harmless, but it is kludgy.

John R. Hayes				john@aplcen.apl.jhu.edu
Applied Physics Laboratory
Johns Hopkins University