mkent@violet.berkeley.edu (06/23/87)
Well, I've been messing around with the 1.3 release of Metacomco's
Cambridge Lisp for a couple of weeks now, so I thought I'd drop a line to
tell anyone who's interested what I've seen, and ask anyone who's
knowledgeable one serious question.
Summary: Looks like the result of a graduate class project written by
folks who've never actually written anything substantial in lisp. If I
were in any way connected with this project, I'd be very embarassed now.
Still, if you want compileable lisp on the amiga, what other choice do you
have?
In many ways the 1.3 release is the same as 1.0, with mangled, shitty
documentation, brain-damaged default syntax tables, and NO break package
whatsoever. (However, the lisp supports the creation of and discrimination
between ~10 different types of cons cells, called "acons", "bcons" etc.
Why you might want to make use of such a facility is something I haven't
been able to figure out yet...) Why we had to wait almost two years between
1.0 and 1.3 is another big mystery; the image date in 1.3 is from late
*1985*, 3 months younger than 1.0. The earlier version had a half-baked
"resident" structure editor; rather than improve that editor, they've just
thrown it away (i.e. 1.3 has NO editor).
On the plus side, the compiler seems to do a reasonable amount of
optimization (at least it eliminates tail-recursion) and the compiled code
is pretty fast. The big pluses of this system are the pluses of lisp in
general, which include the ability to freely intermix compiled and
interpreted code.
A key problem with cambridge lisp is that it was written for the 68000,
and it's never known anything about the amiga (e.g. NO graphics, NO sound,
NO windows...) There was a very narrow, low-level system interface in 1.0,
but its apparent inconvenience of use was rendered academic by the fact
that it just plain didn't work. In 1.3, it works. As my father says, "far
out."
This system interface consists of a pair of functions that let you call
routines in opened libraries, passing the functions the lib base ptr, the
offset of the routine entry, and a vector of args to be stuffed into D0-3
and A0-3 (if you want to use other registers, you're screwed, but that's
irrelvant unless you want to call something arcane like CreateProc or
anything involving a bitblt...) This seems like a reasonable way to access
system routines, but there seems to be one big hole in it: there are no
(documented) functions which do a general "peek" or "poke."
So, for instance, you can open a window by opening the intuition lib and
calling the OpenWindow routine (I felt real clever when it occured to me to
build a NewWindow struct to pass it by concatenating the struct together as
a string, byte by byte) and the routine will return the base address of a
Window struct. But now, if you want to do something with the window, like
draw on it, you need the address of the RPort. You can get the address of
that address by just adding 50 to the window address, but there you're
stopped, because there's no way to read the contents of that address! So,
while you're able to call system routines, there doesn't seem to be any
support for parsing the structures the sytem builds (and returns pointers
to).
I'm currently getting around this with a horrible kludge: I've written C
programs to do peeks and pokes, taking their args from the command line
*and writing the result to a special file in ram: * When I want to do one
of these operations from lisp, I Execute the appropriate routine, open and
read the file, close the file and return the value!! Yuck.
SO, HERE'S MY BIG QUESTION: DOES ANYONE KNOW HOW TO DO A PEEK OR A POKE
FROM CAMBRIDGE LISP??
I would be more than glad to have anyone come out and tell me what a
jerk I am for putting down cambridge lisp; how there are obvious ways to do
these things I'm asking about. Any suggestions of any kind will be greatly
appreciated...
By the way, I'm trying to do some real work in cambridge lisp, and I'm
evolving a body of code, including a simple window package and some file
tools... Let me know if you're also interested in building some kind of
workable *environment* around lisp on the amiga, perhaps we can get
something together...
Marty Kent
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MKent@violet.berkeley.edu
School of Education / 4527 Tolman Hall / UC Berkeley / Berkeley, Ca. 94720
415/ 642 0288
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