Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!rochester!pt.cs.cmu.edu!dsl.pitt.edu!pitt!willett!ForthNet
From: ForthNet@willett.pgh.pa.us (ForthNet articles from GEnie)
Newsgroups: comp.lang.forth
Subject: Vectored Execution
Message-ID: <1485.UUL1.3#5129@willett.pgh.pa.us>
Date: 9 Aug 90 00:18:05 GMT
Organization: String, Scotch tape, and Paperclips.  (in Pgh, PA)
Lines: 45

Category 18,  Topic 67
Message 3         Tue Aug 07, 1990
D.RUFFER [Dennis]            at 23:03 EDT
 
Re: boris@prodigal.psych.rochester.edu (Boris "cull" Goldowsky)

 > 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.

Although, as Mitch mentioned, Forth does not contain any "standard" way to
recover space from selected definitions, you can simulate the feature in just
about any Forth.  Define a "buffer" for each definition that you want to be
able to redefine.  Something like this:
        256 CONSTANT MAX-BUFFER ( -- n   P: Largest definition )

        : FOO ;   MAX-BUFFER ALLOT

Note that I do not include the definition header in the FOO buffer. This is to
prevent a looping link structure that I can't think of any other way to solve
right now.

Then you need a way to redefine the word.  You could redefine : if you want,
but I'll choose a name like this:

        : REDEFINE   HERE  ' >BODY DUP H !  ]
                MAX-BUFFER + HERE < ABORT" Exceeded buffer"
                H ! ;

Of course, this may not work with all Forths, especially those who do already
have memory recovery schemes.  Also, if you do get the error message, it is
likely that you will not be able to recover since the next definition's header
has been corrupted.  However, if you are just looking for something simple and
you don't have a large set of definitions that need to be redefined, this
might just suite your needs.

I should also warn you that I just typed this in off the top of my head.  If
you have trouble with it, IT DOES NOT WORK!  So don't hold me liable for any
damages resulting from its use.  :-)

DaR
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