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=> Date: Wed, 29 May 91 15:00:02 GMT
=> From: Doug Philips
=>  <cis.ohio-state.edu!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!pitt!willett

=> Subject: Object Oriented Forth..
=> I don't think you've made the case for having to have long hyphenated
=> names.  And reverse polish is the nature of Forth.
                                     ^^^^^^^^^^^^^^^
It is, in fact, one of it's strengths. It makes things simple.

=> > Another quick note:  In a true object oriented system the objects are
=> > created unbound and float on the stack until they are either no longer
=> > needed (90% of the cases) or are bound to a name.  I haven't seen
=> > too many FORTH OOP's that do this (but then again I haven't seen too
=> > many FORTH OOPS!).

Good point. But that's not part of the OOS, it's just an way of handling
things. I *really* prefer named objects, i.e., Objects would return already
known objects, instead of creating new ones.

=> The question is really one of what OOP oughta look like in Forth.
=>
=> OOP requires knowing the types of things.
=>      Forth is traditionally untyped.

Knowing types? No. OOP requires that only methods defined for an object have
access to it's data fields. I handle this with vocabularies. A class is a
vocabulary. It's methods data fields are defined inside this class, so only
this methods can have access to the fields (Of course one could get-order, but
it doesn't matter). The fields are allocated with a special word, like ARRAY.
No types. What then happens?
MESSAGE -- Creates a word that gets an object from stack and search for himself
in this object, executing then the associated CFA. The object have it's value
saved.
OBJECT: -- Creates a vocabulary, initialize some variables, and creates a word
with these values. A VALUE will keep the address of this word so that the words
bellow can change the values.
METHOD: -- Get the following word (an already defined MESSAGE), and save the ID
of the message and the CFA (returned by START:) at HERE. (Changes OBJECT or
CLASS). Then it START:s.
When the object is executed, it leaves an value on the stack. When MESSAGE is
executed, it gets this value, saves it, and search for METHOD in a list
somewhere in Object. When Method is finally executed, all the references to the
object's data (just offsets) is added to the start of the data area of the
Object (whose value it's known). No types. It's just a complex DEFERred word.

=> OOP usually requires automatic memory management.
=>      Forth is traditionally very flexible in letting you roll
=>          your own memory management.

Automatic doesn't mean you can roll your owm memory management. In fact, if you
don't want one of the kinds I offer to you (static, dynamic and virtual), you
can do your own without changing anything else.

=> Therefore adding OOP to Forth is _not_ just adding a few new defining
=> words (object, class, message, whatever), but requires an integrated

Right.

=> effort to achieve a typed _and_ memory managed system onto which an OOP
=> can be added.  That is, if you want to go the whole nine yards and have

Wrong. The memory management system can be yours. And you don't need types.
Inheritance, hidden data fields and everything else can be obtained by just
another level between you and the machine. ALLOT won't just ALLOT, it will keep
the size and the offset of this. Things like that.

Maybe I can post some words (< 3Kb of source with documentation) that enables
you to use objects, although without Inheritance.

=> -Doug
=> ---

                              (8-DCS)
Daniel C. Sobral



Mon, 15 Nov 1993 04:32:00 GMT  
 
 [ 1 post ] 

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