Merge of the "new ByNeed" branch

[Raphael Collet]

Denys wrote:

> > Maybe it is simpler to synchronize on Y before binding R.  The following
> > avoids the creation of a second read-only, without breaking semantics:
> > (...)
> 
> I like this better, but I think it has a slight bug when P might
> actually wait until Y becomes needed.  Instead, I would make Y needed
> right away:

You're perfectly right.  I'll keep your version as a backup if I cannot
complete the optimized version.

> >  - {ByNeedFuture P X} could use the same technique as ByNeed above.
> >    Simply make X a read-only with a cheap suspension that creates a
> >    thread whenever X becomes needed.
> 
> If you think about it, my suggestion is a trivial specialization of
> your idea: make a read-only-like variable with one slot (aka your
> suspension) for P.  It's a lot easier than your more general scheme
> and we could have it fairly soon.  It could be replaced by your more
> general scheme when it becomes available.

I can implement it if someone gives me a hint.  I know how to push a
call statement in a thread, but I don't know how to push a try-catch
statement, as ByNeedFuture requires.  Can somebody help me?

> > Kevin and I don't think those have to be done for the upcoming
> > release.  Maybe for 1.3.1...
> 
> Of course, but if we could have them (or at least an optimized
> ByNeedFuture) that would be so much nicer :-)

Okay, I'll examine this closer.

Thanks a lot for your comments, Denys.


Cheers,

raph
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