From: Francis Cianfrocca <garbagecat10@...>
Date: 2006-09-09T05:53:21+09:00
Subject: Re: state machine in ruby

On 9/8/06, ara.t.howard@noaa.gov <ara.t.howard@noaa.gov> wrote:
 >
>
>      harp:~ > cat a.rb
>
>      require 'fsm'
>
>      FSM.system do
>
>        fsm{
>          states %w( empty full )
>          transition 'filling', 'empty' => 'full'
>          transition 'emptying', 'full' => 'empty'
>        }
>
>        observer{
>          on_entry 'empty' do
>            puts 'became empty.'
>
>            transition 'empty', 'filling' do
>              puts 'filling...'
>              sleep 1
>            end
>          end
>
>          on_entry 'full' do
>            puts 'became full.'
>
>            transition 'full', 'emptying' do
>              puts 'emptying...'
>              sleep 1
>            end
>          end
>        }
>
>        start
>      end
>
>      STDIN.gets
>


Reading this, I kept trying to figure out how this is different from
plain old yacc, then I realized you have no lookahead capability. What
kind of situations have you used this in? I don't understand Chris'
example enough yet to decide if it constitutes a regular language or
something more.

Mechanically dealing with comms protocols is a pretty interesting
subject, although in general the more recent ones aren't terribly
complicated. (The practical subset of HTTP isn't bad; SIP isn't bad;
SMTP is a bear; XML is ambiguous in at two places I know of.) I often
end up just writing recursive-descent parsers that expose their
internal state and use a pushback buffer so they can be restarted.