From: Ben Tilly <ben_tilly@...>
Date: 2001-02-21T01:54:01+09:00
Subject: [ruby-talk:11178] Re: RFC: RubyVM (long)

Mathieu Bouchard <matju@cam.org> wrote:
>
>On Tue, 13 Feb 2001, John van V. wrote:
[...]
>"Writing L in L" is called metacircularity.
>
>For as long as I've been thinking about writing a compiler, I've
>considered metacircularity as an essential feature.  This was in 1995 or
>so... The idea was already pretty common in the 80's.  That Perl people
>begin to talk about it now is pure coincidence (or not).

The idea is, of course, much older than that.  The
first interpreted language that I know of was Lisp.
The first Lisp interpreter was written in Lisp, and
then that was unexpectedly translated into assembly,
turning Lisp from a theoretical language into a
practical reality:

http://www-formal.stanford.edu/jmc/history/lisp/node3.html

> > There was also talk of attaching various interperters (translators?) to 
>a
> > single VM,
>
>I am interested in modular interpreters more than in adding translators
>for other languages, but the former allows for the latter.

I suspect that the original idea was mine.  I suggested
that if the front end and back end for Perl were being
made independent anyways, then the front end should be
made pluggable.  This is an extension of hacks like
Lingua::Romana::Perligata (accept source-code that looks
like Latin).  I am not sure it is a good idea (in fact I
called it a bad idea whose time may have come), but it
certainly is an interesting one.

> > (presumably the perl one) using expertise from blackdown, python, etc.
>
>I doubt you'll be able to make, say, Ruby and Perl and Java people
>agree on something about a common runtime environment.

Absolutely.

Perl and Ruby use hashing as a low level construct.  Java
does not.  This is one reason that the Java VM can be
faster than Perl's internal VM, but real programs written
in Perl can still be faster than equivalent programs in
Java - the Perl programs use hashing.

Perl's scalars are hideous beasts.  Basically a scalar can
switch between types essentially at will, and an SV will
store what the value is as a string, number, etc at the same
time to speed this up.  Scalar values in Ruby are far, far
simpler since everything is a straightforward object.

So there we have technical differences in the VMs for all
three that reflect visible language differences which I do
not think are going away at any time soon.

>BTW, I don't think "virtual machine" is an appropriate word to describe
>anything in what I want to do.

Virtual machine can be used to mean virtually anything.
Can't you stretch the term to fit what you want? :-)

Cheers,
Ben
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