class protocol_switch_processor :(string * Netplex_types.processor) list ->Netplex_types.processor
(proto_name, proto_proc). All mentioned
      processors are merged into a single processor. When a TCP connection
      arrives, it depends on the protocol which processor is actually
      activated. (Every socket is bound to a protocol, so this can be derived
      from the socket.)
      It is up to the user whether the merge makes sense.
