Features/foreach parallel construct

[kikofernandez]

Add foreach parallel construct that iterates over an array and executes the iterations in parallel (by using tasks behind the scenes). You cannot assume that the side-effects of the foreach construct have been applied (finished) by the end of foreach construct.

E.g.

class Main
  def main(): void {
    let master = new Master()
        a = [1, 2, 3, 4, 5]
    in 
      foreach item in a {
        master.add(item)
      }
  }

It's tested under Mac and Linux (vagrant) and has documentation. Feedback is welcome! :)

[supercooldave]

There seems to be two tests, but only output for one of them.
Have you tested cases such as: array has size 0, nested foreach loops?
Can you assign back into the array?

[kikofernandez]

@supercooldave:
one test is edited since it uses the keyword foreach as the name of the function and foreach is now a reserved keyword.

1. at the moment, I was assuming that the array had all the elements. the size of an array is known at compile time, and I am not sure that we have a construct for checking how many slots of the array are filled. Good catch.
2. No nested loops as of now either, I can check on that if you think it's important.
3. You cannot assign back at the moment, but if you would like that to be the default behaviour, I can fix it so that it returns either the array with all the items fulfilled (no futures) or the array with futures or get creative!

[supercooldave]

Re 1: I didn't mean that the array had uninitialised entries -- that's quite challenging to check, so let it be the programmer's problem.

Re 2: Nested loops can come later, but it will be important.

Re 3: What is the default behaviour (I haven't read the manual)?

[supercooldave]

It also seems that in now becomes a keyword.

[kikofernandez]

in was already a keyword, wasn't it? We have the let ... in

[kikofernandez]

Re Re 3: the body of the foreach is transformed into an async { body }

[supercooldave]

Re re re 3: D'oh!

[kikofernandez]

Re Re 3: the body of the foreach is transformed into an async { body }

[supercooldave]

Re Re 3 (2): So you are saying, indirectly, that there is an array of futures returned, or what?

[kikofernandez]

Re Re 3 (3) there's nothing returned at the moment. it's similar to using just the async for each iteration and not keeping the future. A foreach construct does not usually return anything, that would be a map, that's why I thought that we should be consistent with its semantics.

[supercooldave]

The semantics is fine. I just wanted to know what it is.

[kikofernandez]

Not sure where we stand right now... 1 is no issue, 2 will come later and 3 means that a foreach construct returns unit type. Is there something that I should fix? (I'll create 2 as an issue as soon as this gets merged)

[supercooldave]

Nothing to fix. Maybe add a test case for empty arrays.

[supercooldave]

I get the following warning
foreach_construct_src/Main.encore.c:30:19: warning: incompatible pointer types passing '_enc__active_Master_t *' (aka 'struct _enc__active_Master_t *') to parameter of type 'pony_actor_t *' (aka 'struct pony_actor_t *') [-Wincompatible-pointer-types] pony_traceactor((*((struct _enc__task0_env_task*) p)).master);

I will merge as it passed all the tests (except the three pesky ones), but perhaps you should check that wraning