Push-based runtime + access to collections in code blocks

[neilconway]

This program is executed in a weird manner in the push-based runtime:

  class PushPredicates
    include Bud
    state do
      table :t_in
      table :t_out1, [:a, :b, :c]
    end
    bootstrap{t_in <= [[1,1],[2,2]]}
    bloom do
      t_out1 <= (t_in*t_in).lefts do |t1|
        ['inc', 'inc', t1.key] if t_in.pro{|t| puts "t = #{t}"; [t.key]}.include? 1
      end
    end
  end
  def test_predicates
    p = PushPredicates.new
    p.tick
    assert_equal([['inc', 'inc', 1], ['inc', 'inc', 2]], p.t_out1.to_a)
  end

Prior to a recent checkin, calling pro on t_in in the body of the join would result in creating additional wirings at runtime, which definitely doesn't seem sound. However, now that we've changed BudCollection#pro to call @storage.pro when called outside wiring, this program doesn't produce the expected results (t_out1 is empty).

We should consider whether to support such programs, and if so, what the best approach is.