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From: Salvador Mirzo <smirzo@example.com>
Newsgroups: comp.misc
Subject: Re: Alan Kay on OOP
Date: Mon, 17 Mar 2025 20:42:26 -0300
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ram@zedat.fu-berlin.de (Stefan Ram) writes:

> Salvador Mirzo <smirzo@example.com> wrote or quoted:
>>I've read the Early History of Smalltalk, by the way.  I think I
>>understand what he means by ``messaging'', ``local retention and
>>protection'' and ``hiding of state-process''.  My knowledge reaches its
>>limits a bit in ``extreme late-binding of all things'' and I get
>>certainly puzzled in ``it can be done in Smalltalk and in LISP'' given
>>that he is ``not aware of [others]''.
>
>   Object-oriented programs contain expressions to describe the sending
>   of messages at runtime. Here's an example of such an expression:
>
> o s: x
>
>   . "o" is the receiver object, "s" the selector (keyword) of the
>   message, and x is an argument.
>
>   "Extreme late-binding of all things" to me (S. R.) means
>   that it is possible to give the the values of "o" and "x"
>   (including their types) only as late as immediately before
>   "o s: x" is being evaluated (executed).

Thanks.  That makes sense!

>>Now, to address my main puzzle.  The email is from 2003.  Alan Kay was
>>certainly aware of Python, Java and so on.  Why would his notion of OOP
>>be impossible in Python or Java?
>
>   He might have some criteria he has not mentioned.

Okay.  I thought there was something obvious to some that I didn't know.

>   For example, in Smalltalk, blocks of code are objects, too,
>   and you can define your own custom bool type and "if" statement
>   using Smalltalk and such blocks. Maybe he requires that, in
>   an object-oriented language, blocks of code are objects, too. [1]

Interesting.  What is the class of these objects that are blocks of
code?  (Thanks for the awesome example in [1].)

>   In LISP, you can have code values using "LAMBDA", and maybe
>   that's the criterion Alan Kay used, as both Smalltalk and LISP 
>   have code block as run-time values.
>
>   In Python and in Java there also are non-object-oriented features,
>   and maybe he requires that, in an object-oriented programming
>   language, everything has to be done in an object-oriented way;
>   what might be called a "/pure(ly)/ object-oriented language".

Yeah---that makes sense to me.  Maybe he requires that really everything
must be an object, including code blocks.  So I guess Smalltalk and LISP
are the purely object-oriented languages---or at least the first ones.

>   [1]
>
>   So, you define two classes "True" with
>
> ifTrue: aBlock
>   ^aBlock value
>
>   and "False" with
>
> ifTrue: aBlock
>   ^nil
>
>   . Now we have implemented an if statement using polymorphism
>   that can be used as:
>
> a > 0 ifTrue: [a := 0]
>
>   . I have not checked this code on a Smalltalk implementation.
>   Maybe it needs some additions or modifications, but it gives
>   the general idea.
>
> An attempt to emulate this in Python:
>
>   main.py
>
> class True_:
>     def if_true( self, block ):
>         exec( block )
>
> class False_:
>     def if_true( self, block ):
>         pass
>
> class Boolean_:
>     def __new__( self, value ):
>         return True_() if value else False_()
>
> a = -2; Boolean_( a < 0 ).if_true( "print( 'It is true!' )" )
> a = +2; Boolean_( a < 0 ).if_true( "print( 'It is true!' )" )
>
>   output
>
> It is true!

Very cool!  Thanks for the example!