again pingpong, send and whereis

[elsbiet]

executing

-module(pp).

-export([start/0, ping/1, pong/0]).

ping(0) ->
    pong ! finished,
    io:format("ping finished~n");

ping(N) ->
    pong ! {ping, self()},                                  % this does not work
    %   whereis(pong) ! {ping, self()},                         % this works
    io:format("ping sent~n"),
    receive
        pong ->
            io:format("Ping received pong~n")
    end,
    ping(N - 1).

pong() ->
    receive
        finished ->
            io:format("Pong finished~n");
        {ping, Ping_PID} ->
            io:format("Pong received ping~n"),
            Ping_PID ! pong,
            pong()
    end.

start() ->
    register(pong, spawn(pp, pong, [])),
    spawn(pp, ping, [3]),
    receive X -> X end.

results in

Starting application...
ping sent
 -- no more output--

replacing

    pong ! {ping, self()},                                  % this does not work

with

   whereis(pong) ! {ping, self()},                   % this works

results in the expected output:

Starting application...
ping sent
Pong received ping
Ping received pong
ping sent
Pong received ping
Ping received pong
ping sent
Pong received ping
Ping received pong
ping finished

btw:

replacing io:format("..~n") by erlang:display("..) results in

Starting application...
"ping sent""Pong received ping"

"Ping received pong"
"ping sent""Pong received ping"

"Ping received pong"
"ping sent""Pong received ping"

"Ping received pong"
"ping finished"

rgds, g.