A method of operating a computer according to an actor model, the method comprising: defining a plurality of actors, each taking form of a data structure comprising respective data and one or more respective functions for operating on the respective data; generating a wrapped message to be transmitted from a transmitting actor to multiple recipient actors, the wrapped message comprising at least one constituent message, a sorted list of the recipient actors, and an index indicating an entry in the list, the index initially being set to indicate the first recipient actor in the list; transmitting the wrapped message from the transmitting actor to the first recipient actor in the list; each of the recipient actors, except the last in the list, upon receiving the wrapped message, advancing the index and forwarding the wrapped message to the next actor in the list as indicated by the advanced index.