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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Things that OO programming lacks
Date: Mon, 17 Nov 2014 21:44:32 +0100
Organization: cbb software GmbH
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Xref: news.eternal-september.org comp.lang.ada:23487
Date: 2014-11-17T21:44:32+01:00
List-Id: <comp.lang.ada>

On Mon, 17 Nov 2014 12:21:42 -0700, Shark8 wrote:

> On 17-Nov-14 10:28, Dmitry A. Kazakov wrote:
>> FSM are proven to be extremely
>> complex to use, error-prone and unmaintainable. That is because states are
>> as uncomposable as events are. If you add new or remove old states you are
>> in deep trouble.
> 
> Not really; in Ada we'd just say:
> 
> Type Event is ( 'a', 'b', 'c', 'd' );
> Type State is ( Start, middle_1, middle_2, Stop );
> 
> Type Transition_Table is array (Event, State) of State;
> 
> Type FSM(<>) is private;
> Function  Create( Transitions : Transition_Table ) return FSM;
> Procedure Do_Event( State_Machine : in out FSM; Action : Event );
> 
> private
>    Type FSM(Transitions : not null access Transition_Table) is record
>      Current : State:= Start;
>    end record;
> 
> -- in the Body ...
> 
> Function Create( Transitions : Transition_Table ) return FSM is
> ( Transitions => New Transition_Table'(Transitions), others => <> );
> 
> Procedure Do_Event( State_Machine : in out FSM; Action : Event ) is
> begin
>    case Action is
>     when others => null; -- Attach particular/special actions here.
>                          -- Also allow Ada to do case-coverage where
>                          -- possible.
>    end case;
> 
>    State_Machine.Current:=
>       State_Machine.Transitions(Action, State_Machine.Current);
> end Do_Event;

In Ada you can implement Post-Turing machine in few lines. Should we run to
redesign everything in the tape language?

However my personal favorite would be Brainfuck, it should be 100-200 lines
in Ada. Have fun!

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de