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From: kjx@comp.vuw.ac.nz (R James Noble)
Newsgroups: comp.lang.smalltalk
Subject: Smalltalk Implementation Queries.
Message-ID: <1989Nov30.001121.29195@comp.vuw.ac.nz>
Date: 30 Nov 89 00:11:21 GMT
Sender: news@comp.vuw.ac.nz (News Admin)
Reply-To: kjx@comp.vuw.ac.nz (R James Noble)
Organization: Victoria University of Wellington, Wellington, New Zealand
Lines: 85


In the process of attempting to write a Smalltalk virtual machine and
compiler I have come across some quirks of Smalltalk and I would like
to know what an implementation _should_ do. I am also interested in
the opinion of some experienced Smalltalkers as to any changes or
additions to Smalltalk that they might consider useful.

I have access to both the Apple Lisa Smalltalk port, an Tim Budd's
Little Smalltalk, items (a..c) below refer to these implementations.

a) cascade message sends .. 

 foo bar baz ; barf

 Is the message barf send to (foo bar), as per Blue book and Lisa, or
(foo bar baz), like little Smalltalk ?
	
b) blocks

 The [Miranda] article describes the standard problems with Smalltalk
blocks. Is it worth the effort to make blocks fully reentrant and use
standard static linkages? Are block temporaries a good idea?  (Lisa
implementation doesn't, Little Smalltalk copes with some tail
recursion)

c) modifying literals.

 The method tmp below.

tmp | a | 
	a _ #( 1 1 1 ).
	a at: 2 put: ( a at: 2 ) + 1.
	^a.

Three invocations will return (1 2 1) (1 3 1) (1 4 1). Would an
implementation that returned (1 2 1) for all invocations be a bug or a
feature. (Both Little Smalltalk and Lisa Smalltalk modify the literal
each time).

d) multiple inheritance.

[Borning] describes a multiple inheritance scheme which is (I
understand) now standard in ParcPlace Smalltalk. Is this now
considered a standard part of Smalltalk? Could another implementation
of multiple inheritance be substituted.

e) class library

How much does a Smalltalk class library need to conform to the Blue
Book in order for the system to be usable as a Smalltalk? Which of the
following categories could be redesigned without losing the feel of
Smalltalk?

Numbers and Magnitudes.
Collections.
Files and Streams.
BitBlit graphics. 
Window System - MVC (Smalltalk/V has altered this).
User Interface - browsers, inspectors.
Kernel - classes and metaclass hierarchies. (Little Smalltalk modifies this)
Kernel - contexts and processes. (Little Smalltalk modifies this)
System Compiler & Support. (Little Smalltalk modifies this)

f) other strange "features"

- instance variable access only by message send (as per [Ungar]),
	with syntactic sugar to allow Smalltalk methods to compile.
- support for one-of-a-kind objects.
- altered metaclass hierarchy (a class would be a one-of-a-kind object)
- multiple global namespaces (a.k.a. packages)
- object destructors - when an object is garbage collected it can
	cause a message to be sent, for example to deallocate an
	external object (such as an X window).
- anything else you can think of. 

Please reply by mail; I will summarise if necessary.
--
[Miranda] BrouHaHa - A Portable Smalltalk Interpreter, OOPSLA87, p354
[Borning] Multiple Inheritance in Smalltalk-80, AAAI28
[Ungar] Self: The Power of Simplicity, OOPSLA87, p227
--
R James Noble
Computer Science Department
Victoria University, Box 600, Wellington 1, New Zealand
kjx@comp.vuw.ac.nz 		     ...!uunet!vuwcomp!kjx