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From: LEVITT@MIT-OZ
Newsgroups: net.works
Subject: WORKS Digest   V5 #24
Message-ID: <2075@topaz.ARPA>
Date: Thu, 23-May-85 03:39:59 EDT
Article-I.D.: topaz.2075
Posted: Thu May 23 03:39:59 1985
Date-Received: Fri, 24-May-85 04:34:51 EDT
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Organization: Rutgers Univ., New Brunswick, N.J.
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From: LEVITT%MIT-OZ@MIT-MC.ARPA


I have been quietly enjoying Doug Pardee's defense of assembly
language.  I've hacked Lisp Machine lisp quite alot, and I've hacked
assembler, and in some ways I've found assembler more satisfying.

Doing real-time music applications, I've generated some gorgeous
polyphony easily in real time in assembler -- whereas in Zetalisp I'd
almost HAVE to pre-compute it, or strenuously cache it, or give it up.
In general (or at least until recently) system sources were always
available for lispms, so IN PRINCIPLE I could make code perform, even
if it meant microcoding; but the programming style most ENCOURAGED by
the lisp machine system always meant low performance.  (My main
experience is with MIT's old CADR/LM-2 design, but comments about the
programming environment and style apply to today's systems, too.)

Between mediocre compilers, huge operating system kernels, and demand
paged systems, this is typical of HLL environments: you get some good
tools but you lose control of the performance of the machine.

So I think a relevant question is: how much can we improve assembly
code design, maintenance, and debugging tools?  Could we make them so
wonderful that most of the HLLers' objections go away?  (I once heard
a rumor this was being done for the Mac.)  Of course, many assembly
systems already have better source level debuggers than the C and
other compiled HLLs on the same machine.  And, two advanced systems
come to mind:

(1) Jim Dunion's amazing debugger for the Atari (circa 81 -- I forget
its name) was window-based, had an animated stack trace, break window,
etc.  It preceded the Lisp Machine window debugger, and ran faster.

(2) MacNosy by a fellow named Jarmusche (sp?) should have been an AI
degree, if he doesn't already have one.  It "decompiles" 68000 code,
doing a recursive tree walk through apparent code segments, and
allowing the user to intervene.  So you can study and (by entering
macros as you discover structure) grok jump tables and other weird
programming habits of your favorite compilers or assembly code
authors.

Roger Duffey did some interesting work on assembler expertise at MIT's
AI lab a few years ago, but in general it seems to be a vastly
underexplored field.  I think indirectly, the commitment here to
microcoded Lispms killed interest in it.  (Except I hear Richard
Greenblatt did a very smart microcompiler for his Lispms.)

--David Levitt