[e-lang] multiway when-catch

[Rob Withers]

----- Original Message ----- 
From: "Kevin Reid" <kpreid at mac.com>


> On Oct 29, 2007, at 15:36, Rob Withers wrote:
>>> From: "Kevin Reid" <kpreid at mac.com>
>>> I think your promiseSet corresponds to the components produced by
>>> promiseAllFulfilled, which multiway-when uses, as you will see in
>>> the expansion. I recommend that you simply compile/translate
>>> promiseAllFulfilled.emaker to your platform, as it is entirely non-
>>> primitive and well-designed.
>>
>> I was unable to find promiseAllFulfilled.emaker, but I am still
>> looking.
>
> esrc/org/erights/e/elang/interp/

Cool.  I also liked promiseAllResolved.emaker, which is what I have actually 
duplicated.  I also send whenResolved:, but I don't check for broken refs.

>>> Particularly, there should not be any weak references involved, so
>>> GC is irrelevant.
>>
>> I have strong references.  I think I may have fixed the problem I
>> was having by passing the promiseSet as an argument to the
>> #whenResolved: msgs I send to each promise.   I am now resolving
>> the promiseSet and getting into the block.
>
> This sounds like inadequate facets. What authority does a promiseSet
> grant to its holders? If it includes the promises it holds, then this
> is wrong, as the promises should not learn of each other by being
> used together in a when.
>
> Could you explain what a promiseSet is? It does not sound like any
> concept that exists in E, and so I am suspicious of its necessity. Is
> it primitive?

A promiseSet is a list of promises.  I have refactored it to look very much 
like promiseAllResolved.emaker.  Since we can't have standalone functions, I 
needed to add #whenResolved: as a method somewhere.  It holds a collection 
of promises and offers this protocol:

% eventualRef
    "Add an eventualRef to the list"
    refs add: eventualRef.

initialize
    refs := OrderedCollection new.

whenResolved: reactor
    | countDown |
    countDown := refs size.
    refs do: [:each |
        each whenResolved: [:aRef |
            countDown := countDown - 1.
            countDown <= 0
                ifTrue: [reactor valueWithArguments: refs asArray]]].




>
>> One other question I had, I once saw code that conditioned a
>> promise to resolve within a certain timeout, otherwise it broke.
>> Do you happen to know code that could do this?
>
> The final example (building on previous ones) in <http://
> www.erights.org/elang/concurrency/race.html> .

Awesome!  Thanks,

Rob