Question

I have these code

start() ->
    spawn(?MODULE, init, [self()]).

init(From) ->
    spawn(?MODULE, broadcast, []).    

broadcast() ->
    Msg = "helloworld",
    timer:sleep(10000),
    broadcast().

When I test these code in Erlang shell, it give me undef error, I need to export broadcast function, I am just refuse

Answer 1

Code

spawn(?MODULE, init, [self()]).

means you will spawn process which initial call will be ?MODULE:init(self()) or more precisely equivalent of apply(?MODULE,init,[self()]). ?MODULE is macro evaluated to current module name but anyway It is external function call so this function have to be exported even there is ?MODULE used. In contrary

spawn(fun() -> init(self()) end).

is spawn with initial call to the func fun() -> init(self()) end which calls init/1 with result of function self(). It is local call which means init/1 may not be exported. There is another issue with it when self() is performed inside new process so you have to write

Self = self(), spawn(fun() -> init(Self) end).

to achieve same effect as in spawn(?MODULE, init, [self()]) where self() is evaluated as parameter of spawn/3.