Hello World Process Chain

accumulators.erl

-module(accumulators).
-export([average/1]).

average(X) -> average(X, 0, 0).

average([H|T], Length, Sum) ->
	average(T, Length + 1, Sum + H);

average([], Length, Sum) ->
	Sum / Length.

accumulators_shell.txt

Erlang R14B02 (erts-5.8.3) [source] [64-bit] [smp:8:8] [rq:8] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.3  (abort with ^G)
1> c(accumulators).
{ok,accumulators}
2> accumulators:average([1,10,100]).
37.0
3>

hello_world.erl

-module(hello_world).
-compile(export_all).

main() ->
  
  HelloPid = spawn(fun() -> hello_node(none) end),
  WorldPid = spawn(fun() -> world_node(none) end),
  PrintPid = spawn(fun() -> print_node() end),
  
  io:format("Send link messages~n"),
  HelloPid ! {next, WorldPid},
  WorldPid ! {next, PrintPid},
  io:format("Sent messages~n"),
  HelloPid ! {message, "I say"},
  ok.


hello_node(NextPid) ->
  receive
    {next, Pid} ->
      io:format("Hello Process (~p) linked to ~p~n", [self(), Pid]),
      hello_node(Pid);
    {message, Message} ->
      io:format("Hello Process (~p) receices message (~p)~n", [self(), Message]),
      NextPid ! {message, string:concat(Message," Hello")},
      hello_node(NextPid);
    Message ->
      io:format("Hello Process (~p) receives unknown message (~p)~n", [self(), Message])
  end,
  ok.

world_node(NextPid) ->
  receive
    {next, Pid} ->
      io:format("World Process (~p) linked to ~p~n", [self(), Pid]),
      world_node(Pid);
    {message, Message} ->
      io:format("World Process (~p) receives message (~p)~n", [self(), Message]),
      NextPid ! {message, Message ++ World},
      world_node(NextPid);
    Message ->
      io:format("Hello Process (~p) receives unknown message (~p)~n", [self(), Message])
  end,
  ok.

print_node() ->
  receive
    {message, Message} ->
      io:format("Print Process (~p) receives message (~p)~n", [self(), Message]),
      print_node();
    Message ->
      io:format("Print Process (~p) receives unknown message (~p)~n", [self(), Message])
  end,
  ok.

hello_world2.erl

-module(hello_world2).
-compile(export_all).

main() ->
  
  HelloPid = spawn(fun() -> hello_node() end),
  WorldPid = spawn(fun() -> world_node() end),
  PrintPid = spawn(fun() -> print_node() end),
  
  io:format("Send link messages~n"),
  HelloPid ! {next, WorldPid},
  WorldPid ! {next, PrintPid},
  io:format("Sent messages~n"),
  HelloPid ! {message, "I say"},
  ok.


hello_node() ->
  receive
    {next, Pid} ->
      io:format("Hello Process (~p) linked to ~p~n", [self(), Pid]),
      hello_node(Pid);
    Message ->
      io:format("Hello Process (~p) receives unknown message (~p)~n", [self(), Message]),
      hello_node()
  end,
  ok.

hello_node(NextPid) ->
  receive
    {message, Message} ->
      io:format("Hello Process (~p) receives message (~p)~n", [self(), Message]),
      NextPid ! {message, Message ++ " Hello"},
      hello_node(NextPid);
    Message ->
      io:format("Hello Process (~p) receives unknown message (~p)~n", [self(), Message]),
      hello_node(NextPid)
  end,
  ok.

world_node() ->
  receive
    {next, Pid} ->
      io:format("World Process (~p) linked to ~p~n", [self(), Pid]),
      world_node(Pid);
    Message ->
      io:format("Hello Process (~p) receives unknown message (~p)~n", [self(), Message]),
      world_node()
  end,
  ok.

world_node(NextPid) ->
  receive
    {message, Message} ->
      io:format("World Process (~p) receives message (~p)~n", [self(), Message]),
      NextPid ! {message, string:concat(Message, " World")},
      world_node(NextPid);
    Message ->
      io:format("Hello Process (~p) receives unknown message (~p)~n", [self(), Message]),
      world_node(NextPid)
  end,
  ok.

print_node() ->
  receive
    {message, Message} ->
      io:format("Print Process (~p) receices message (~p)~n", [self(), Message]),
      print_node();
    Message ->
      io:format("Print Process (~p) receives unknown message (~p)~n", [self(), Message])
  end,
  ok.

output.txt

..
25> c(hello_world).    
{ok,hello_world}
26> hello_world:main().
Send link messages
Sent messages
Hello Process (<0.140.0>) linked to <0.141.0>
World Process (<0.141.0>) linked to <0.142.0>
Hello Process (<0.140.0>) receices message ("I say")
ok
World Process (<0.141.0>) receices message ("I say Hello")
Print Process (<0.142.0>) receices message ("I say Hello World")

pattern.erl

-module(pattern).
-compile(export_all).

%% pattern matching

greet(male, Name) ->
    io:format("Hello, Mr. ~s!~n", [Name]);

greet(female, Name) ->
    io:format("Hello, Mrs. ~s!~n", [Name]);

greet(_, { FirstName, LastName }) ->
    io:format("Hello, ~s ~s!~n", [FirstName,LastName]);

greet(_, Name) ->
    io:format("Hello, ~s!~n", [Name]).

%% generic

head([H|_]) -> H.
second([_,X|_]) -> X.

%% bits

rgb(<<Red:8,Green:8,Blue:8>>) ->
        {Red, Green, Blue}.


%% guards

old_enough(X) when X >= 16 -> true;
old_enough(_) -> false.

pattern_shell.txt

Erlang R14B02 (erts-5.8.3) [source] [64-bit] [smp:8:8] [rq:8] [async-threads:0] [hipe] [kernel-poll:false]

Eshell V5.8.3  (abort with ^G)
1> c(pattern).
{ok,pattern}
2> pattern:greet(male,"Jack").
Hello, Mr. Jack!
ok
3> pattern:greet(female,"Jill").
Hello, Mrs. Jill!
ok
4> pattern:greet(alien,"Paul").
Hello, Paul!
ok
5> pattern:greet(male,{"Tarn", "Barford"}).
** exception error: bad argument
     in function  io:format/3
        called as io:format(<0.25.0>,"Hello, Mr. ~s!~n",[{"Tarn","Barford"}])
6> pattern:greet(whatever,{"Tarn", "Barford"}).
Hello, Tarn Barford!
ok
7> pattern:head([1,2,3]).
1
8> pattern:second([1,2,3]).
2
9> pattern:rgb(<<16#FF00FF:24>>).
{255,0,255}
10> pattern:old_enough(10).
false
11> pattern:old_enough(20).
true