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From: tsaari@tukki.jyu.fi (Antero Taivalsaari)
Newsgroups: comp.lang.forth
Subject: Re: ... and zen there were objects.
Message-ID: <1990Aug15.071510.3363@tukki.jyu.fi>
Date: 15 Aug 90 07:15:10 GMT
References: <1990Aug7.081509.2315@idacom.uucp> <1498.UUL1.3#5129@willett.pgh.pa.us>
Sender: tsaari@jyu.fi
Organization: University of Jyvaskyla, Finland
Lines: 50

In message <1498.UUL1.3#5129@willett.pgh.pa.us> (Doug Philips) writes:

>What I think is wrong with Object Oriented Extensions to Forth:
>
>All the OOEF's I have seen so far involve active objects or messages
>or both.  By active I mean that the words are IMMEDIATE words.
>
>Take for example Pountain's system as described in his book. ...

My personal opinion is that Pountain's book - although it is
rather well written - is not that good in the object-oriented sense. 
However, his earlier paper in JFAR (vol 3, nr 3, 1986, p.51-73) 
introduces much more elegant object-oriented extensions to Forth. 
In these extensions, the syntax for message sending is:

	PushArg PushArg Object \ message

The word '\' is a special message operator that simply takes 
an address from the top of stack and considers it as the receiver 
of the message. By using this solution, the receiver object and
the message need not have any syntactic relationship to each other.
It is very easy to pass objects around in the system, since 
they can be referred to by simple addresses.

By using this kind of solution, you can easily have anonymous objects;
also, you can easily write words that return objects on the top of the
stack (both of these are, indeed, VERY fundamental operations in 
object-oriented programming).

I have been programming with these kind of OOP extensions to
Forth about three years now, heavily extending and modifying 
Pountain's original code and I am quite convinced that this is the 
right way to do message passing in Forth. However, if a more postfix 
solution is desired, an alternative syntax could also be (as you suggest):

	PushArg PushArg " message" Object SEND

Again, 'SEND' is a special word that simply takes an address
from the top of stack and considers it as the receiver of the message.
'Message' is a string whose address will also be passed to the 
message operator 'SEND'. In Pountain's JFAR code, this kind of 
solution is used internally by the system; however, in his code
message strings are first hashed to integers to improve the efficiency 
of late binding.

Regards,

Antero Taivalsaari
University of Jyvaskyla, Finland
tsaari@jyu.fi