Being human in the Digital age

ing ProtocolsBrief as it is, the Erlang implementa-tion of sequences is much longer andless clear than the original Java ver-sion. Much of the code is not particu-lar to sequences, however, so it shouldErlang value, and it is sent atomicallyand immutably. The message is sent tothe receiving process’s mailbox, andthe sender continues to execute—itdoes not wait for the receiving processto retrieve the message.A process uses the receive expres-sion to extract messages from its mail-box. It specifies a set of patterns andassociated handler code and scansthe mailbox looking for the first mes-sage that matches any of the patterns,blocking if no such message is found.This is the only blocking primitive inErlang. Like the patterns in functionclauses, the patterns in receive op-tions match structures and bind newvariables. If a pattern uses a variablethat has already been bound to a value,then matching the pattern requires amatch with that value, as in the valuefor Sequence in the receive expressionin get_next/1.The code here implements a simpleclient-server protocol. In a call, the cli-ent process sends a request messageto the server process and blocks waitfigure 2: server.erl.