Re: Are state machines just for parsing?

[dragonchild]

in reply to Are state machines just for parsing?

What kind of interface / API would you be interested in seeing? How would you want to use said module?

The reason I ask is that I've built state machines for several projects and they were different enough that I don't think I could've used a generic solution / framework. For example, I've used state machines to

• perform actions in a basic scripting language
• handle events that have been defined to fire when X occurs
• be the engine for a web application (both before I found CGI::Application and with it)

It's kinda like trying to build a module for the Schwartzian Transform or the Guttman-Rosler Transform (GRT). It's good to know the pattern, but making a generic version just complicates the matter. Or, put another way, we'd almost have to write another mini-language to have a state machine. And, we already have that with regexes.

[samtregar]

What kind of interface / API would you be interested in seeing?

I see two phases. First, I need an API to lay out the network. For my purposes each state has to have:

• A unique name
• A description
• A list of possible next states
• Code which runs when the state is reached
• Code to determine if this state should be the next one

I don't know what this API should look like. Maybe each state is a Perl module implementing a few methods. Maybe it's just a big data structure made of hashes and arrays. Whatever it is it has to be easy to change later when the businessmen change their minds.

Next I need to give the machine a starting state and an event. The machine should either tell me what the next state is or produce an error if the event doesn't trigger a valid next state. Something like:

   $next_state = $machine->run($state, $event);

-sam