Good morning!

POE was written for a particular need (a VM for a multitasking, multi-user object repository and runtime environment), and it turned into something that lives in an area of computational theory that I didn't know a whole lot about. Documenting it has been really hard.

About examples: POE's distribution includes about 300KB of examples and tutorials. See the twenty-some programs in its samples/ directory and their summaries in the main POE manpage.

The big deal? I don't know enough to say, but here's a list of links which may help explain some concepts:

• Foldoc's definition of "abstract machine".
• Foldoc's definition of "finite state machine".
• Foldoc's definition of "virtual machine".
• An introduction to abstract state machines.
• An excellent list of abstract machine sites.
• Concurrent State Machine Software Architecture Styles
• UML for Real-Time Systems Design

If you figure it out first, let me know! :)

-- Rocco Caputo / troc@netrus.net

Just out of curiosity, how would you say POE compares to Libero?

That strikes me as a similar ideal, though not Perl specific. (I have not tried it, but I have used the Xitami webserver that they wrote with it and it works...)

Thanks,
Ben

Cheers,
KM

Libero is a finite machine meta-language. It includes a tidy state machine description language and a very nice engine for generating real source code from it. It comes with schemas to make machines in C, REXX, x86, several other languages, and even Perl. I like it a lot.

POE is very much a library: code is built with it rather than in it. It also lives at a lower conceptual level: it's abstract state machines rather than any particular kind. This is both a blessing and a curse.

Implementation differences abound: Libero's machines are intended to encompass entire programs; POE's are components that work together by passing message events. Libero's machines are sequential, while POE's are concurrent. Libero's states don't accept parameters; POE's do. Libero doesn't generate a transition/event queue, and POE has one. The list goes on and on.

That said, I still like Libero and it's not at all incompatible with POE. If anything, POE's currently not finite machine enough for Libero, so I'm working on a POE::DFA (deterministic finite automaton) that will make it easier to finish a schema I've been tinkering with. After that I expect to be able to churn out state machines like crazy, which is why I went looking for something like Libero in the first place.

Oh, if anything, POE probably is more like iMatix's SMT (Simple Multi-Threading kernel), which is an add-on for Libero and also part of Xitami. I must admit that I haven't given SMT a really close look, so I may be totally wrong.

-- Rocco Caputo / troc@netrus.net / :)

In a current endeavor, I am starting to use POE. Admittedly, it's because I don't feel like writing a state machine plus a server; however, it appears that POE seems to make this a bit easier by providing a framework. Of course, it feels a bit like wrapping oneself around MPW, Metrowerks, RogueWave, or MFC, but still it's a decent framework.

I am curious as to the performance of the beastie in a production environment, as opposed to writing a simpler graph used as a callback table, triggered on transitions, vis-a-vis NerveCenter et al.

I do believe that writing drop-in components will become easier once I write a more generic Component loader -- or at least settle on a well-defined directory/folder structure for the packages --, since to achieve such ease of extensibility, the Component/Filter/Wheel paradigm must evolve to a new abstraction, such as a generic plug-in with a set directory OR package structure. Just as we tend to write -- or some variant thereof -- ...

pacakge Foo;

sub new {
  my $this = shift;
  my $class = ref($this) || $this;
  my $self = {};
  bless $self, $class;
  return $self;
}

1;
[download]

...so too will we see the likes in POE.
-v
"Perl. There is no substitute."

I do believe POE makes implementation of event based programs more easier than some of the other frameworks that your mentioned that I have used e.g. MFC. As of right now it might lack some functonality of the big boys but I feel its getting there. As for writing a state engine from scratch, perl says dont re-invent the wheel. If its out there just plug it in. I too am trying some intresting things with POE. Will keep you updated on how it goes.

POE is important, and more people should be using it. I would like to find a qualified and interested person to write an article (or a series of articles) about POE to be published on www.perl.com. The author would, of course, be paid.

If you're interested, please send me email (mjd@plover.com)

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have you ever seen a commie drink a glass of water?

learn to stop loving the bomb today (don't be so uptight)