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From: mikpa@massormetrix.ida.liu.se (Mikael Patel)
Newsgroups: comp.lang.forth
Subject: Incapsulation and visibility in Forth
Message-ID: <1@massormetrix.ida.liu.se>
Date: 2 Aug 89 14:05:48 GMT
Organization: Dept of Comp. and Info. Science, Univ. of Linkoping, Sweden
Lines: 50

Hi, Forth-world, I am doing some work on comparing Forth with other
programming languages with regard to incapsulation and visibility 
of symbols (Forth: words).

Basically Forth seems to have only have these methods:

1) The "compilation" and "interpretation" mode mark as for words
   such as "if" which is marked as only usable during compilation
   and then always executed.

2) The use of vocabularies. This does not generally solve the 
   problem of visibility of words as all words defined in a 
   vocabulary are visible by a "user".

3) Don't care about internal words as these are allowed to be
   redefined.

The problem of incapsulation and visibility has come some what of
the main attributes of a programming language because of all 
the "noise" around object-orientation.

What I would like to propose is the following three words, similar
to "immediate", as mode markers to give Forth a more well defined
notion of incapsulation and visibility.

private ( -- )
	Marks the most recently created dictionary entry as a word
	which is only available in the dictionary it is created in.
	The word is not available when the dictionary is not current.

execution ( -- )	
	Marks the most recently created dictionary entry as a word 
	which is only available in execution mode.
	
compilation ( -- )
	Marks the most recently created dictionary entry as a word 
	which is only available in compilation mode.

So compilation words like "if" become:

: if ( flag -- ) .... ; compilation immediate

So what do you say Forthians? Seen something like this or maybe 
an other approach! Tell us about it!

Mikael Patel

   'Just the place for a Snark! I have said it thrice:
      What I tell you three times is true.' 
	- Lewis Carrol -