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From: jimc@iscuva.UUCP
Newsgroups: net.lang.forth
Subject: Re: Information Hiding in FORTH
Message-ID: <242@iscuva.UUCP>
Date: Mon, 14-Jul-86 19:54:42 EDT
Article-I.D.: iscuva.242
Posted: Mon Jul 14 19:54:42 1986
Date-Received: Fri, 18-Jul-86 00:57:12 EDT
References: <12110@amdcad.UUCP> <622@uvacs.UUCP>
Reply-To: jimc@iscuva.UUCP (Jim Cathey)
Organization: ISC Systems Corporation, Spokane, Wa.
Lines: 37

> I have been recently thinking of a way to implement something like the
> 'C' static scoping type in forth.  This would allow a word or group of
> words to use a VARIABLE without letting the VARIABLE be visible outside
> the group; something like:

I believe map-Forth (Michael A Perry's version for my old CompuPro 68000)
included the words:

INTERNAL
 <<boring and/or dangerous words to be hidden here>>
EXTERNAL
 <<the visible stuff>>
MODULE     (actually does the work)

I recall that both INTERNAL and EXTERNAL merely left addresses on the 
data stack, and that MODULE patched the vocabulary search chain to
miss the internals.  Woe be unto him whose internal or external definitions
which (on purpose or not) swallowed any of the data stack or left any extra!
Other than this caveat, I thought the idea and the implementation were
really first-class -- only a tiny bit of code.

As a side note, compressing the headers might not always be a good
idea, since the same Forth package had a tracer (hooked into NEXT) that
printed out the names of the currently executing words and the top few
values on the stack.  I had a few words with headers missing that always
screwed up the trace output.

-- 

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! II      CCCCCC !  Jim Cathey
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