[self-interest] Re: Self bytecodes
David.Ungar at Eng.Sun.COM
Tue Jun 1 23:02:47 UTC 1999
This is a great idea!
In fact I have already done some of it.
I wrote an interpreter and had it running on my Mac, up to running
Are you local?
We could get together and talk about this sometime.
In fact, the Self bytecodes are quite bad for interpretation.
The interpreter had to count colons at every send.
You would need a different bytecode set to take this approach too far.
(I have chosen instead to retarget the NIC -- still a lot of work.)
At 8:58 AM -0300 6/1/99, Douglas Atique wrote:
>jecel at lsi.usp.br wrote:
>> > It all seems fine, but I don´t understand something seemingly
>> > straightforward: knowing that in a send the receiver and arguments are
>> > popped off stack and the result is pushed onto stack, how is the number
>> > of arguments of a send determined, so that my interpreter could know how
>> > many pops it should make? It seems that in the fast_compiler, when the
>> > machine code for a send is generated, the information of number of
>> > arguments is kept somewhere. Where?
>> You can just count the number of ':' characters in the selector name,
>> and that is the number of arguments. Except that if the selector name
>> is composed of special characters, then we have a binary selector and
>> there is one argument.
>All right, but the parser might already have done that, in fact the
>fast_compiler code generation reads this arg_count from somewhere.
>> Testing this at every message send is *very* inefficient - the
>> Smalltalk bytecodes encode the number of arguments in the send
>> bytecode itself. But since the Self bytecodes were meant to be
>> compiled away, this wasn't considered a problem.
>What I want to do is to switch the compiler, assembler and runtime (part of,
>that is) off, plug in an interpreter in every point where this whole subsystem
>is used and be able to compile it under Solaris x86 or Linux by
>defining in the
>makefile something like -DPORTABLE, for example.
>I mean, my interpreter is to interface directly with the method objects
>generated by the parser, not to replace the parser. This would be a temporary
>solution to the problem of portability, introducing the inefficiency of the
>interpreter. Perhaps this is because I miss the old time when I ran OS/2 2.1
>with 4MB RAM :-)
>> For an interpreter, there isn't a good solution if you are going
>> to use a standard Self world. If you don't mind creating your own,
>> slightly different, world you could separate canonical strings
>> representing selectors into different "types". One way to do this
>> would be to add a constant slot indicating the number of arguments
>> when you canonicalize a string. That way, 'last' would have a
>> constant slot with the value 0, while for 'between:And:' that
>> slot's value would be 2. This slot would always be in the same
>> place in the string's map (if you don't make any other changes)
>> so your interpreter can easily access it.
>sma at netsurf.de wrote:
>> >It all seems fine, but I don´t understand something seemingly
>> >straightforward: knowing that in a send the receiver and arguments are
>> >popped off stack and the result is pushed onto stack, how is the number
>> >of arguments of a send determined, so that my interpreter could know how
>> >many pops it should make?
>> You can derive that from the selector symbol. Unary selectors (that are
>> selectors composed from letters - especially the first character must be a
>> lowercase letter - without ':' in it) need no arguments at all. Binary
>> selectors (that are all selectors which neither start with a letter or with
>> an '_') have exactly one argument. For keyword selectors (which are
>> composed of sequences of letters (and digits) that end with a colon ':')
>> simply count the number of colons.
>> A different problem is to know when to pop returned objects from the stack
>> which aren't used. I think, you cannot detect that and simply adjust the
> > stack when you leave the method. Here's an example: 3+4. nil
>> This will generate something along: push 3, push 4, send #+, push nil.
>> The + method for integers will pop both 3 and 4 from the stack and push the
>> result, 7. However, this object isn't needed and will use one stack slot
>> upton the method returns (with nil).
>> There might be a way to notice that "7" isn't used anywhere in the method,
>> but that's probably to much work for an interpreter. A compiler that will
>> create and analyse a complete parse tree for each method can do this.
>Well, Stefan, I am using the following principle to get to do something about
>The Self Group has already done a lot to prove Self to be efficient. Now
>someone should make it portable. This won't be straightforward if one wants to
>incorporate all the benefits of the adaptive compilation, so I want to make
>Self run slowly on an x86-platform in a way such that the VM code can be
>compiled for SPARC, MIPS, Acorn, etc. Of course, the FIRST step is to
>neutralize the processor dependency, so after that we'll have code that is
>still dependent on the operating system. This is why I have chosen Solaris x86
>as my development platform (it could have been Linux, but I wanted
>to make sure
>there would be the least difference possible from Solaris SPARC). It is the
>same as the original environment in which Self ran, but the processor is
>different. Next step will be to "make glue" for other systems. You can see the
>example of Java, they have first provided a UI class library that
>written for each platform (the heavyweight components), then they evolved by
>providing Swing, which is platform-independent and the platform-dependent part
>of the code is reduced to windows (don't take this too precisely, it
>can we do, by rewriting code that is implemented as primitives in Self.
>In fact, before that I would like to study more carefully the primitives
>available to define a minimal primitive set, perhaps a "microkernel VM" :-)
>Jecel's ideas about the Squeak Smalltalk system, in which much more is
>implemented in the language itself than in Self, make much sense to the
>evolution of Self in my opinion.
>Thanks for your comments and ideas.
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