Re: stackless language features

Lenard Lindstrom <[email protected]> Tue, 29 Jun 2004 10:31:21 -0700 (Pacific Daylight Time)
Newsgroups	gmane.comp.lang.prothon.user
Message-ID	<Mahogany-0.66.0-4294655545-20040629-103856.00@pop3.norton.antivirus>
On Mon, 28 Jun 2004 18:08:34 -0700 Mark Hahn <[email protected]> wrote:

> I was going to start this thread in the new Prothon wiki (
> http://prothon.org/wiki ) as our first thread there, but when I created my
> first page, it crashed so I don't think it's ready for prime-time.
> 
> As our class discussion starts to wind down (hopefully), it is time to wind
> up our discussion of stackless language features.  I'll start the discussion
> by giving some links to previous messages containing my proposal,
> Christian's comments when he first joined our list, and Paul's thread about
> continuations.  Read these over and give your ideas for implementing
> stackless features in Prothon.
> 
> This is the last actual stackless proposal (before Christian joined us):
> http://www.prothon.org/pipermail/prothon-user/2004-June/002124.html
> 
> This is a thread-kill proposal.  Later I found out that Ada works the same
> way so I assume this will be approved by everyone without argument:
> http://www.prothon.org/pipermail/prothon-user/2004-June/002125.html
> 
> This is the thread when Christian first joined our list.  It covers several
> topics but it discusses stackless also.
> http://www.prothon.org/pipermail/prothon-user/2004-June/002146.html
> 
> This is a long thread where Paul argues for having real continuations in
> Prothon.
> http://www.prothon.org/pipermail/prothon-user/2004-June/002108.html
> 
> This is my ultimate response to Paul.  I basicly try to weasle out of the
> issue by saying that we will eventually have continuations but not now:
> http://www.prothon.org/pipermail/prothon-user/2004-June/002199.html
> 
> As always if you don't make your own proposal I will and you know how bad
> mine are :-)
> 
This is very tentative:

Declaring a thread or generator:

thread <name> (arg, ...):
    <body>

An enhanced yield statement can return a value.

A generator example:

thread fib(n):
    """Return first n Fibonacci numbers"""
    sum, prev = 1, 0
    for i in n:
        yield sum
        sum, prev = sum + prev, sum

iter = fib(5)
for i in iter:
    print(i)

In this case thread just replaces the gen keyword.

A more general example:

thread handlerA(obj):
    print(yield obj)
    print(rval)

thread handlerB(obj):
    print(A(obj))

A = handlerA.thread()
A.start(1)            # Enters wait state on yield
B = handlerB.thread()
B.start(2)
#    May print
# 1
# 2
#    or
# 2
# 1

Explicit calls on active thread objects take precidence over yield
to avoid deadlocks.

Lenard Lindstrom
<[email protected]>