Tasks in Encore

Here is a tentative fibonacci number calculation in Encore using a strawman task library design:

class Fib
  def fib(n:int) : int 
    if n < 2 then n else 
       let 
         x = 0
         y = 0
       in {
         finish {
           async { fib(n - 1) }
           async { fib(n - 2) }
         }
         x + y 
       }

This uses X10 style async and finish which becomes less elegant with the way we handle local variables. In any case, I am proposing to push async and finish primitives. Here is how we could write the program in a better way using a let-like finish construct:

class Fib
  def fib(n:int) : int 
    if n < 2 then n else 
       finish
         x = async fib(n - 1)
         y = async fib(n - n)
       in 
         x + y 

One important question is how to integrate with the actor-driven parallelism of PonyRT. The following is a strawman proposal for this:

Dave's comment

My feeling was that the task lib was something that went on under the hood, as the target of (some) running closures and the party types.

The core above code could be expressed something like, assuming that reduce exists:

reduce (+) (fib (n - 1) | fib n)

or, synchronising first, then calling sequential foldl:

foldl (+) (sync (fib (n - 1) | fib n))