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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: ADA CORE TECHNOLOGIES ANNOUNCES GNAT-TO-JAVA SYSTEM
Date: 1997/09/20
Message-ID: <dewar.874761008@merv>#1/1
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References: <dewar.873998738@merv> <34196E8E.1790@gsfc.nasa.gov>
 <dewar.874165896@merv> <341D47EE.3804@gsfc.nasa.gov> <dewar.874439071@merv>
 <342002F1.6913@gsfc.nasa.gov> <dewar.874622854@merv>
 <34228A59.7D45@pseserv3.fw.hac.com>
Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-09-20T00:00:00+00:00
List-Id: <comp.lang.ada>


Wes says

<<As one of those people, I would like to say that, from experience
with the UCSD p-System (including reverse assembling the Z-80
interpreter when support was not available), and having read the
JVM specs, I do not have the misconceptions you speak of.  I just had
the motivation that IF it could be done, one would automatically
get byte-code from several languages instead of just from Ada.
Even a new code generator that used the gcc tree instead of the GNAT
tree would do this.  I recognize that this is a bigger job than
the job ACT is undertaking.  And it's certainly out of reach of my
available time and talent.  But it would still be a Good Thing.>>

No, it would not be a good thing at all. The translation would be at
entirely the wrong level. It would not be possible to interface with
Java, and various Java tools would be useless, since the semantic
level of the JVM generated would be completely wrong. OK, you know
the JVM specs, but perhaps you do not have a clear idea of the semantic
level of a GCC backend, which is a very simple machine model with a
limited number of registers.

If you really think that what you propose is useful (I am quite sure it
is not), then it is pretty trivial to do. Just make a GCC backend that
generates idiotic Java code that simulates a simple machine, and then
compile the Java. So far, no one even thought that was worth doing for
C, let alone Java, because of the semantic mis-match problem, but this
is an easy summer project for some student, and would be quite fun and
instructive (but not useful).

Incidentally the idea that generating JVM from the backend of GCC is
a bigger task than what ACT is undertaking is COMPLETELY wrong. Generaing
a high level translation of Ada semantics to Java semantics is indeed
tricky, especially if you are committed to a validated full-language
system as we are (it is no surprise to us that the Intermetrics system
is not yet validated, we are quite aware of the diffficulties).

By contrast generating silly JVM output from the backend of GCC is by
contrast trivial, and probably no more than a few weeks work. The fact
that you think it is a bigger task must mean you have some major
misconceptions, I can't quite guess what.

Robert