Cannot run a simple application in Erlang - erlang

Question

I wrote a simple application in Erlang, but it refuses to work with the following error:
=SUPERVISOR REPORT==== 18-Jan-2012::15:03:27 ===
Supervisor: {<0.60.0>,my_sup}
Context: start_error
Reason: {'EXIT',{undef,[{my,start,[{8077,none}]},
{supervisor,do_start_child,2},
{supervisor,start_children,3},
{supervisor,init_children,2},
{gen_server,init_it,6},
{proc_lib,init_p_do_apply,3}]}}
Offender: [{pid,undefined},
{name,my},
{mfa,{my,start,[{8077,none}]}},
{restart_type,permanent},
{shutdown,brutal_kill},
{child_type,worker}]
=INFO REPORT==== 18-Jan-2012::15:03:27 ===
application: my
exited: {shutdown,{my_app,start,[normal,[noarg]]}}
type: temporary {error,{shutdown,{my_app,start,[normal,[noarg]]}}}
And the modules:
my.erl
-module(my).
-export([start/2, stop/0]).
start(Port,_arg) ->
io:format("starting my").
stop() ->
ok.
my_app.erl Application module, perform application behavior.
-module(my_app).
-behaviour(application).
-export([start/2, stop/1]).
start(_Type, _Args) ->
io:format("my server starting~n"),
my_sup:start_link().
stop(_State) ->
io:format("my server terminating~n"),
ok.
my_sup.erl Supervisor logic
-module(my_sup).
-behaviour(supervisor).
-export([start_link/0]).
-export([init/1]).
start_link() ->
supervisor:start_link(my_sup, []).
init(_Args) ->
{ok, {
{one_for_one, 10, 60},
[{my, {my, start, [{8077,none}]
},
permanent, brutal_kill, worker, [my]}]}}.
Config file (my.app):
{application, my,
[
{description, "Demo"},
{vsn, "1.0"},
{id, "hello"},
{modules, [my,my_sup]},
{registered, [my,my_sup]},
{applications, [kernel, stdlib]},
%%
%% mod: Specify the module name to start the application, plus args
%%
{mod, {my_app, [noarg]}},
{env, []}
]
}.
I changed child spec like you recommend, but the problem still remains.
=SUPERVISOR REPORT==== 19-Jan-2012::00:34:21 ===
Supervisor: {<0.96.0>,my_sup}
Context: start_error
Reason: <0.97.0>
Offender: [{pid,undefined},
{name,my},
{mfa,{my,start,[8077,none]}},
{restart_type,permanent},
{shutdown,brutal_kill},
{child_type,worker}]
=ERROR REPORT==== 19-Jan-2012::00:34:21 ===
Error in process <0.97.0> with exit value:
{{badmatch,{error,eaddrinuse}},[{my,'- start/2-fun-0-',1}]}
=INFO REPORT==== 19-Jan-2012::00:34:21 ===
application: my
exited: {shutdown,{my_app,start,[normal,[noarg]]}}
type: temporary
{error,{shutdown,{my_app,start,[normal,[noarg]]}}}

Answer 1

The my:start/2 should take two arguments but in the child specification you only give it one argument ({8077,none}). You could change the child spec to:
{my, {my, start, [8077,none]}, permanent, brutal_kill, worker, [my]}
As an aside your indentation and line breaking of the Supervisor Specification is a bit off making it difficult to see what belongs to what.
EDIT: Comment to new error
This is not the same problem as before. You are getting a new error, eaddrinuse, which normally means you are trying to use an IP address/port which is already in use. This would imply you are doing some socket programming in your code.

Answer 2

Your supervisor specifies that my:start should take one argument, but it takes two. You probably want to change the child spec to:
{one_for_one, 10, 60},[{my, {my, start, [8077,none]}

Answer 3

Your my:start/2 provides a wrong return value.
Supervisor expects tuple {ok,Pid}, while your function simply returns ok (the last call is to io:format, which returns ok, so your function also does).
If you want to use a supervisor, you must spawn a new process and link it to the supervisor. For example
start(_) -> {ok,spawn_link(fun() -> io:format("~w started~n",[self()]),timer:sleep(5000),io:format("~w exiting~n",[self()]) end)}.
should do the job for you.