ByNeedFuture revisited

[Raphael Collet]

Denys wrote:

> I would like to make 2 proposals concerning NyNeedFuture:
> 
> 1. it is currently poorly defined because it does not automatically
>    address the issue of escaping exceptions.  I submit that it would
>    be more USEFUL to define it as follows:
> 
>    proc {ByNeedFuture P X}
>       R={NewReadOnly}
>    in
>       thread
>          {WaitNeed R}
>          {BindReadOnly R
>           try {P} catch E then {Value.failed E} end}
>       end
>       X=R
>    end

I like the proposal very much.

> 2. I would like the old futures to be retained SOLELY for the purpose
>    of providing an optimized implementation of ByNeedFuture (and
>    ByNeedDot) where no resource is allocated until the future becomes
>    needed.

Okay, I'll try to make it so.  Kevin had an idea for delaying the
allocation of resource until a by-need computation is needed.
The idea is to create cheap suspensions for that purpose.  I think
it might be a good optimization, and allow us to remove futures.
But that's "future" work ;-)

Cheers,

raph
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