concurrent

-module(server).
-export([rpc/2, loop/0]).
rpc(Pid, Request)->
    Pid ! {self(), Request},
    receive 
	Response->
	    Response
end.
loop()->
    receive
	{From, {re, W, H}}->
	    From ! W*H,
	    loop();
	{From, {c, R}} ->
	    From ! 3.14159 * R * R,
	    loop();
	{From, Other} ->
	    From ! {error, Other},
	    loop()
end.

result:

18> server:rpc(Pid4, {re, 6, 10}).
60