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From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: State Machine Implementation
Date: 1998/08/06
Message-ID: <m3yat3kpna.fsf@mheaney.ni.net>#1/1
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Sender: matt@mheaney.ni.net
References: <35C90369.CFE8ED98@inficad.com>
NNTP-Posting-Date: Wed, 05 Aug 1998 22:47:37 PDT
Newsgroups: comp.lang.ada
Date: 1998-08-06T00:00:00+00:00
List-Id: <comp.lang.ada>

"Ray A. Lopez" <rdsys@inficad.com> writes:

> Does anyone have any implementions of a state machine?  The states would
> be just an enumerated type and I am guessing you would use a case
> statement.  Just looking for more info on how to implement this using
> Ada.

I prefer to implement a state machine using labels and gotos.  That's
how I usually write tasks.  For example:

task body IO_Manager is

   Mode : Missle_Mode;

begin

   <<Idle>> null;

   select
      accept Start;
   or
      accept Stop; 
      goto Idle;
   or
      terminate;
   end select;

   <<Main>> null;

   select
      accept Change_Mode (Mode : Missle_Mode) do
         IO_Manager.Mode := Mode;
      end;

      <transmit mode>
      <make asynchorous read>

      <<Waiting_For_Response>> null;

      select
        accept IO_Completion;
        goto Main;

      or 
        accept ...;
        goto Waiting_For_Response;

      ...


Scanners typically have a state-machine implementation.  I just wrote a
scanner to parse real literals that weren't quite in legal Ada format,
using gotos to skip over optional parts of the lexical expression.