Re: Are state machines just for parsing?

[lachoy]

This is actually what the Workflow module does. (I think someone else mentioned it too.) You can create:

• Actions to move from one state to another (or not change state at all)
• Conditions to see whether the current environment can execute an action (which changes state).
• Validators to check data coming into the system

All of these are simple Perl classes, and because there's a 'context' moving data into and out of the workflow it doesn't care where it's run, and neither do your classes.

I gave a presentation on it a couple months ago to the Pittsburgh Perlmongers that might be helpful, and it comes with working examples, decent docs, some tests, etc.

[samtregar]

That's a cool presentation. And the module looks great... except, why do I have to program Perl inside an XML file? This makes my skin crawl:

<workflow>
     <type>myworkflow</type>
     <state name="INITIAL">
         <action name="upload file" resulting_state="uploaded" />
     </state>
     <state name="uploaded" autorun="yes">
         <action name="verify file" resulting_state="annotate">
              <!-- everyone other than 'CWINTERS' must verify -->
              <condition test="$context->{user} ne 'CWINTERS'" />
         </action>
         ...

I'd be much happier with:

   my $workflow = Workflow::Generator->new(type => "myworkflow");
   $state = $workflow->add_state(name => "INITIAL");
   $state->add_action(name => "upload file", resulting_state => "uploa
+ded");
   $state = $workflow->add_state(name => "uploaded", autorun => "yes")
+;
   $state->add_action(name => "verify_file", resulting_state => "annot
+ate");
   $condition = $state->add_condition(test => \&check_file);

It's more conscise and all the power of Perl is available for making repetitive structures from common data. If I ever decided to use Workflow I think Workflow::Generator would be my first project.

-sam

[lachoy]

Well, the "perl in XML" part is entirely optional and is actually a recent addition. But I like the idea of creating it programmatically and it should be pretty easy, actually. I might swipe this for later -- with credit, of course...