A Ruby implementation of a waterfall control flow thingy.

async.rb

module Async
  class << self
    def waterfall(objects, handler, &block)
      enumerator = objects.each
      prev_result = nil
      run_next = lambda do
        begin
          # onwards!
          prev_result = handler.(enumerator.next, prev_result) do |success|
            success ? run_next.call : block.(false)
          end

        rescue StopIteration
          # done!
          block.(true)
        end
      end
      run_next.call
    end
  end
end