[erlang-questions] bad_return_from_state_function on "3.21 Complex State” of "OTP design principles"

[by]

Yes, it works with:
                [Digit|Rest] ->
                    {keep_state, Data#{remaining := Rest},
                     [30000, {reply, From, ok}]};
Thanks
by
> 在 2017年12月13日，16:19，Guilherme Andrade <g@REDACTED> 写道：
> 
> It seems to be a typo. I believe the intention is to set up an event timeout[1] of 30 seconds, but if so then the timeout interval should be bundled with the call reply  - "{reply,From,ok}" - in order to make it a part of the list of actions to perform.
> 
> Maybe the following will do the trick:
> 
>     {keep_state, Data#{remaining := Rest}, [30000, {reply,From,ok}]}
> 
> [1]: http://erlang.org/doc/man/gen_statem.html#type-event_timeout <http://erlang.org/doc/man/gen_statem.html#type-event_timeout>
> 
> On 13 December 2017 at 08:01, by <by@REDACTED <mailto:by@REDACTED>> wrote:
> Hi,
> 
> I am trying the example on http://erlang.org/doc/design_principles/statem.html#id77558 <http://erlang.org/doc/design_principles/statem.html#id77558>
> "3.21 Complex State”
> 
> But I got exception below:
> ====================================
> Erlang/OTP 20 [erts-9.0] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false] [dtrace]
> 
> Eshell V9.0  (abort with ^G)
> 1> c(code_lock3).
> {ok,code_lock3}
> 2> code_lock3:start_link([1,2,3], 4).
> Locked
> {ok,<0.67.0>}
> 3> code_lock3:button(1).
> Locked
> ** exception exit: {bad_return_from_state_function,
>                        {keep_state,
>                            #{code => [1,2,3],remaining => [2,3]},
>                            30000,
>                            [{reply,
>                                 {<0.60.0>,#Ref<0.235851222.49545217.215838>},
>                                 ok}]}}
>      in function  gen_statem:parse_event_result/8 (gen_statem.erl, line 1318)
>      in call from gen_statem:loop_event/6 (gen_statem.erl, line 1015)
>      in call from proc_lib:init_p_do_apply/3 (proc_lib.erl, line 247)
> 4> 
> =ERROR REPORT==== 13-Dec-2017::15:46:09 ===
> ** State machine code_lock3 terminating
> ** Last event = {{call,{<0.60.0>,#Ref<0.235851222.49545217.215838>}},
>                  {button,1}}
> ** When server state  = {{locked,4},#{}}
> ** Reason for termination = error:{bad_return_from_state_function,
>                                    {keep_state,
>                                     #{code => [1,2,3],remaining => [2,3]},
>                                     30000,
>                                     [{reply,
>                                       {<0.60.0>,
>                                        #Ref<0.235851222.49545217.215838>},
>                                       ok}]}}
> ** Callback mode = [handle_event_function,state_enter]
> ** Stacktrace =
> **  [{gen_statem,parse_event_result,8,[{file,"gen_statem.erl"},{line,1318}]},
>      {gen_statem,loop_event,6,[{file,"gen_statem.erl"},{line,1015}]},
>      {proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,247}]}]
> ====================================
> 
> I think the problem is on this:
> 		[Digit|Rest] -> % Incomplete
> 		    {keep_state, Data#{remaining := Rest, 30000},
> 		     [{reply,From,ok}]};
> Change code to below got the **exception
> 		[Digit|Rest] -> % Incomplete
> 		    {keep_state, Data#{remaining := Rest}, 30000,
> 		     [{reply,From,ok}]};
> 
> Actually, this is apparently wrong, since the map can not got “30000" in this case. I tried move “30000" out of the map, then the above exception occurs.
> And, I also tried just remove the “30000”, and it works fine.
> 		[Digit|Rest] -> % Incomplete
> 		    {keep_state, Data#{remaining := Rest},
> 		     [{reply,From,ok}]};
> 
> My question is:
> Is this a typo in the documentation?
> Or
> Am I missing something?
> 
> Thanks
> by
> 
> _______________________________________________
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> 
> 
> 
> 
> -- 
> Guilherme

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