% Create ZeroMQ context
1> zmq:start_link().
{ok,<0.34.0>}

% Create a ZeroMQ REQ socket and specify that messages
% are delivered to the current shell's mailbox.
2> {ok, S} = zmq:socket(req, [{active, true}]).
{ok,{#Port<0.623>,1}}

% Connect to server
3> zmq:connect(S, "tcp://127.0.0.1:5555").
ok

% Send a message to server
4> zmq:send(S, <<"Test">>).
ok

% Receive a reply
5> zmq:recv(S).
{error,einval}

% Note the error - in the active socket mode we cannot
% receive messages by calling zmq:recv/1. Instead
% use receive keyword to accomplish the task.

6> f(M), receive M -> M end.
% The process blocks because there's no reply from server
% Once you start the server as shown in the following steps
% the receive call returns with the following message:
{zmq,1,<<"Reply">>}

1> zmq:start_link().
{ok,<0.34.0>}
2> {ok, S} = zmq:socket(rep, [{active, false}]).
{ok,{#Port<0.483>,1}}
3> zmq:bind(S, "tcp://127.0.0.1:5555").
ok
4> zmq:recv(S).
{ok,<<"Test">>}
5> zmq:send(S, <<"Reply">>).
ok