Trouble running the example in `ex3-drop-app`

[bmitch]

Going through the book and was trying this example in chapter 11.

I cloned this repo, navigated to the ch11/ex3-drop-app folder and ran the following:

Erlang/OTP 20 [erts-9.2] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V9.2  (abort with ^G)
1> c(drop_app).
{ok,drop_app}
2> code:add_path("ebin/").
true
3> application:load(drop).
ok
4> application:start(drop).
{error,{bad_return,{{drop_app,start,[normal,[]]},
                    {'EXIT',{undef,[{drop_sup,start_link,[],[]},
                                    {application_master,start_it_old,4,
                                                        [{file,"application_master.erl"},{line,273}]}]}}}}}
5> 
=INFO REPORT==== 24-Feb-2018::11:08:42 ===
    application: drop
    exited: {bad_return,
                {{drop_app,start,[normal,[]]},
                 {'EXIT',
                     {undef,
                         [{drop_sup,start_link,[],[]},
                          {application_master,start_it_old,4,
                              [{file,"application_master.erl"},
                               {line,273}]}]}}}}
    type: temporary

Not sure what I am missing? Thanks.

[rustkas]

After c(drop_app). you also have to compile drop_sup and drop_app modules too ( c(drop_sup). c(drop_app). ).
After that application will be started correctly.

7> application:start(drop).
ok
8> gen_server:call(drop, 60).
{ok,34.292856398964496}
9>