pingpong example

etc/pingpong.erl

@@ -0,0 +1,51 @@
+-module(pingpong).
+-export([main/0]).
+
+% this runs two processes and has them talk to each other
+% output:
+%
+% 2> pingpong:main().
+% <0.96.0> received {pong, <0.97.0>, 10}
+% <0.97.0> received {ping, <0.96.0>, 9}
+% <0.96.0> received {pong, <0.97.0>, 8}
+% <0.97.0> received {ping, <0.96.0>, 7}
+% <0.96.0> received {pong, <0.97.0>, 6}
+% <0.97.0> received {ping, <0.96.0>, 5}
+% <0.96.0> received {pong, <0.97.0>, 4}
+% <0.97.0> received {ping, <0.96.0>, 3}
+% <0.96.0> received {pong, <0.97.0>, 2}
+% <0.97.0> received {ping, <0.96.0>, 1}
+% <0.96.0> received {pong, <0.97.0>, 0}
+
+
+main() ->
+    PingerPID = spawn(fun pinger/0),
+    PongerPID = spawn(fun ponger/0),
+    PingerPID ! {pong, PongerPID, 10}.
+
+pinger() ->
+    receive
+        {pong, PID, N} ->
+            io:format("~p received {pong, ~p, ~p}~n", [self(), PID, N]),
+            % ignore once we get to 0 or lower
+            case N > 0 of
+                true  -> PID ! {ping, self(), N-1};
+                false -> ok
+            end,
+            % once we're done, go back to the top
+            pinger()
+    end.
+
+
+ponger() ->
+    receive
+        {ping, PID, N} ->
+            io:format("~p received {ping, ~p, ~p}~n", [self(), PID, N]),
+            % ignore once we get to 0 or lower
+            case N > 0 of
+                true  -> PID ! {pong, self(), N-1};
+                false -> ok
+            end,
+            % once we're done, go back to the top
+            ponger()
+    end.