module EventMachine::Deferrable

Then return arg.
use the supplied block (if any) as the callback.
are defined, then use them. If neither are defined, then
then look at the arguments. If either callback or errback
If arg is deferrable (responds to :set_deferred_status),
If arg is an ordinary expression, then return it.
What's the class of arg?
Evaluate arg (which may be an expression or a block).
--
A future is a sugaring of a typical deferrable usage.

def self.future arg, cb=nil, eb=nil, &blk
  arg = arg.call if arg.respond_to?(:call)
  if arg.respond_to?(:set_deferred_status)
    if cb || eb
      arg.callback(&cb) if cb
      arg.errback(&eb) if eb
    else
      arg.callback(&blk) if blk
    end
  end
  arg
end