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From: jr@LF-SERVER-2.BBN.COM (John Robinson)
Newsgroups: comp.emacs
Subject: Re: parallel gemacs?
Message-ID: <8711132317.AA07361@ucbvax.Berkeley.EDU>
Date: Fri, 13-Nov-87 18:17:25 EST
Article-I.D.: ucbvax.8711132317.AA07361
Posted: Fri Nov 13 18:17:25 1987
Date-Received: Sun, 15-Nov-87 10:57:02 EST
References: <8711131614.AA09484@oxtrap.UUCP>
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: jr@BBN.COM
Organization: The ARPA Internet
Lines: 34

>> Can anyone verify the feasability of lack thereof of a parallel
>> version of gnu-emacs?  What I want to know is, is there a good reason
>> that eval, map*, etc. cannot be done in parallel?  Like, does the
>> existing lisp code presume sequential execution?

Well, this depends on the e-lisp "language definition" (which of
course doesn;t really exist).  And, for the C code, there is most
probably a necessity that things generally happen sequentially.

Lisps of various flavors do provide some functions that make no
guarantees about their evaluation order.  (let ...) versus (let* ...)
for example.  Whether programmers have necessarily followed the rules
in their use of these constructs is another matter.

Parallel garbage collection is an even nastier matter.  Master's
thesis material at least (but don't let this daunt you, please!).

BBN Advanced Computers is working on a parallel Lisp which is based on
MIT scheme; scheme's tighter semantics make it better for parallel
implementation for many of the same reasons it is more tractable for
compilation.  Maybe you could start with the scheme that FSF
distributes.

There are a lot of different ways you can think about for
parallelizing Lisp.  I believe ACI is using the lazy evaluation model
- the result of an expr need not be known until it is needed by
someone else.  This lets you parallelize in, for example, picking up
function arguments.  The trouble, of course, is in side effects.
Again, this is why scheme's semantics are so much of a help, in this
case because they force you to write code that will execute properly
in a parallel environment.

/jr
jr@bbn.com or jr@bbn.uucp