code: def map(self, f):
          
          @self.pipe
          def recver(recver, sender):
              for item in recver:
                  try:
                      sender.send(f(item))
                  except Exception, e:
                      sender.send(e)
          return recver
docs: *f* is a callable that takes a single argument. All values sent on this
          Recver's Sender will be passed to *f* to be transformed::
  
              def double(i):
                  return i * 2
  
              sender, recver = h.pipe()
              recver.map(double)
  
              h.spawn(sender.send, 2)
              recver.recv() # returns 4