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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Ada95 to ANSI_C converter
Date: 1997/04/02
Message-ID: <dewar.859997175@merv>#1/1
X-Deja-AN: 230175678
References: <dewar.859559977@merv> <5htg0a$v8v$1@news.nyu.edu>
 <dewar.859987799@merv> <5htp1a$h1$1@news.nyu.edu>
Organization: New York University
Newsgroups: comp.lang.ada,comp.lang.c
Date: 1997-04-02T00:00:00+00:00
List-Id: <comp.lang.ada>


Richard said

<<I'd view such an effort as creating more of a *tool* that could be used
in various products than as a product itself.>>

Right, that's certainly a reasonable view. One interesting bit of history
here is that at one point in GNAT project we talked about making a backend
that generated the kind of junk C that Richard quoted in his previous
message. The idea was to provide a bootstrap path for systems that lack
GNAT now -- in this scenario, we would distribute the junk c, and people
could compile it on some such system.

However, in practice, the cross-compilation approach has worked very well,
a combination of the basic technology of gcc being strong in this area,
and the internet at work (somewhere, it is likely that there is someone
interested in porting GNAT to machine A, who has access to machine B for
which a GNAT already exists). 

The original ancestor of GNAT for those interested was a SunOS implementation
on Sparc that was bootstrapped using the Alsys Ada 83 compiler. As soon as
that was successfully bootstrapped, the Alsys compiler was permanently 
retired, and all subsequent GNAT implementations for SunOS and all other
systems can trace their heritage to this original bootstrap.

GNAT is on a lot of machines and systems now, and we have the impression
that the requirement to use the cross-compilation path has not been an
impediment. Everynow and then, we get someone who naively acquires the
sources, puts them on a machine with no GNAT, and expects to be able to
build GNAT -- not such a surprising mistake, since this approach will work
for pretty much all other GNU software which is written in C.

At first, we felt it was important to make this true of GNAT now, but as I
say, it seems from experience like this is not a critical issue. I really
can't think of a single case of a machine for which GNAT does not exist,
and would exist if it could be moved in this manner. Sure there are machines
for which GNAT does not exist (even a few for which GCC does not exist), but
the cross-compilation does not seem to be the barrier in such cases.

Robert Dewar