[e-lang] multiway when-catch

[Rob Withers]

Hello again!

I've revived my work on SqueakElib and I am trying to implement the multiway 
when-catch.  I have #whenResolved: and #whenBroken: defined and that is how 
I specify a when-catch; when-catch is not part of the language I use.  I 
suppose my first question is: is when-catch defined in terms of 
#whenResolved: and #whenBroken:?  If so, what does it look like?

Here is what I see as an example of the multiway when-catch in Walnut:

 # E syntax
 def maxTempVow := vehicleSpecsRcvr <- getMaxEngineTemperature(carType)
 def engineTempVow := carRcvr <- getEngineTemperature()
 when (engineTempVow,maxTempVow) -> {
     if (engineTempVow > maxTempVow) {println("Car overheating!")}
 } catch e {println(`Lost car or vehicleSpecs: $e`)}

and here is the equivalent syntax I am trying to support (Dining 
Philosophers example):

 (self leftDispenser getFork % self rightDispenser getFork)
  whenResolved: [:lFork :rFork |
   self leftFork: lFork.
   self rightFork: rFork.
   self startEating];
  whenBroken: [:lFork :rFork |
   self error: 'error getting forks'].

where #getFork returns an eventualRef and the #% message concatenates 
promises to create a promiseSet.  Unfortunately, nothing holds onto the 
promiseSet so it is getting GCed.  I suspect that I need to pass the 
promiseSet as an argument to #whenResolved: msgs sent to each promise, but I 
am not sure how.

I seem to recall an example of how to impl this using #whenResolved:, but I 
can't find it.  I may have been thinking of the resolveAllVow example, in 
Walnut,  but that is specified in terms of when-catch-finally.  Another 
thing that may help me is the elang code that defines when-catch.

Cheers,
Rob