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From: barmar@think.com (Barry Margolin)
Newsgroups: comp.object
Subject: Re: The Emperor Strikes Back
Message-ID: <1991Feb23.075248.10519@Think.COM>
Date: 23 Feb 91 07:52:48 GMT
References: <3351@sequent.cs.qmw.ac.uk> <ALMS.91Feb22151210@ministry.cambridge.apple.com>
Sender: news@Think.COM
Distribution: comp.object
Organization: Thinking Machines Corporation, Cambridge MA, USA
Lines: 34

In article <ALMS.91Feb22151210@ministry.cambridge.apple.com> alms@cambridge.apple.com (Andrew L. M. Shalit) writes:
>In article <3351@sequent.cs.qmw.ac.uk> steve@cs.qmw.ac.uk (Steve Cook) writes:
>   The killer is 'lexically-scoped'.
>I agree with Steve.  In object-oriented programming, the meaning of an
>identifier (message or variable) depends on the reciever (which is
>part of the run-time program state).  This is essentially a
>disciplined form of dynamic binding.  It's very different from lexical
>binding, in which the meaning of an identifier can be derived purely
>from the surrounding program text.

I believe the lexical scoping referred to is the implementation of
instances as procedures that remember their instance variables in lexical
variables, e.g.:

(define (make-frob iv1 iv2 iv3)
  (lambda (operation args)
    (cond ((eq operation 'set!-iv1)
	   (set! iv1 (car args)))
	  ((eq operation 'iv1)
	   iv1)
	  ...
	  ((eq operation 'sum)
	   (+ iv1 iv2 iv3)))))

(set! my-frob (make-frob 1 3 5))
(my-frob 'iv1 nil) => 1
(my-frob 'set!-iv1 '(4))
(my-frob 'sum nil) => 10

--
Barry Margolin, Thinking Machines Corp.

barmar@think.com
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