larry@JPL-VLSI.ARPA (12/06/86)
--This is being sent to the entire news group because this question keeps
coming up.
First, I'd strongly advise you NEVER to use an unvalidated Ada compiler. I
have in the past and I've seen others do it. Ada is still new enough so that
even the experts occasionally have to work out just what is legal--as seen
on this distribution list. Teaching or learning erroneous information that
you have to later unlearn is very costly of our scarcest resource: human
skill and enthusiasm. So stay away from Janus, Artek, General Systems, etc.
That leaves only two products that will run on PCs. The NYU Ada/Ed interpreter
is only $95 and has very readable diagnostics. If you're going to teach a class
buy a copy of it and duplicate it as necessary (check the license--I think this
duplication is legal). Performance is not very good, obviously, but for an
intro course I believe it's acceptable. It will run on XTs and compatibles
with a hard disk and 640K memory. Also, if you can execute code single-step it
might be better than a compiler for debugging code. (Anyone on this
list who might discuss this product more?)
The other choice is the Alsys Ada compiler, which runs on an AT and produces
object code that can run on an XT as well as the AT. (On the AT it can run in
either real or virtual mode, limited by 640K or 16M bytes of memory--all from
MS-DOS). I've been using it recently and I consider it a good system, but
still far from perfect. At Ada Expo Alsys was promising a major rewrite of this
product that would improve overall compilation performance several times. (You
can get 100 lines per minute but at the cost of an extra memory board on which
you store your source and the compiler intermediate work files.) They also
promised very improved performance of the executable in several areas that are
still too slow, including tasking. Be sure to buy the $360 maintenance contract
so you'll get these updates when they become available, which I estimate to be
mid-87. As of now, as long as you do fairly vanilla programming, the Alsys
compiler will deliver performance about like that of decent C compilers.
If you do get the Alsys compiler ($3000 including a 4M memory board that will
run at 8 MHz) I strongly suggest you buy their AdaPROBE symbolic debugger.
It supposedly allows you to view source code and perform cross-referencing of
identifiers so you can find other places in the code where the identifier is
being used, a very useful feature. (I've only seen demos of the debugger, so I
can't vouch for its usefulness.)
Larry @ jpl-vlsi