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From: wmb@MITCH.ENG.SUN.COM
Newsgroups: comp.lang.forth
Subject: Re: Files VS Blocks, a compromise
Message-ID: <9010191326.AA15531@ucbvax.Berkeley.EDU>
Date: 19 Oct 90 02:09:12 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: wmb%MITCH.ENG.SUN.COM@SCFVM.GSFC.NASA.GOV
Organization: The Internet
Lines: 41

>       1.  Make allot a deferred word.  Whenever a programmer develops

You need to defer HERE along with ALLOT .

Unfortunately, Forth's ALLOT is poorly conceived, because you have to
get the address with HERE *before* you tell ALLOT how much data you need.
This pretty much kills the possibility of implementing ALLOT with MALLOC ,
constraining the data space to be contiguous.

In all my recent code, I declare data structures with:

        BUFFER:  \ name  ( size -- )  ( Child: -- adr )

Example:

        100 BUFFER: FOO

        FOO 100 44 FILL

The simplest implementation is:

        : buffer:  \ name  ( #bytes -- )
           create allot
        ;

A more sophisticated implementations might look like:

        : buffer:  \ name  ( #bytes -- )
           create allocate-memory  ,  does> @
        ;

Another variation, which could be SAVE-FORTH'ed would link all buffers
into a static chain and automatically allocate their memory at startup
time.  The variation I use in the Sun firmware automatically allocates
the memory the first time the data structure is accessed.

Which definition of BUFFER: to use depends on the system constraints
(ROM vs. RAM, serially-reusable or not, etc).  Applications are insensitive
to the implementation of BUFFER: .

Mitch