Build simple rules-based state machines in Perl
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FSA/Rules version 0.36

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FSA::Rules implements a simple state machine pattern, allowing you to quickly build rules-based state machines in Perl. As a simple implementation of a powerful concept, it differs slightly from an ideal DFA model in that it does not enforce a single possible switch from one state to another. Rather, it short circuits the evaluation of the rules for such switches, so that the first rule to return a true value will trigger its switch and no other switch rules will be checked. (But see the strict attribute and parameter to new().) It differs from an NFA model in that it offers no back-tracking. But in truth, you can use it to build a state machine that adheres to either model--hence the more generic FSA moniker.

FSA::Rules uses named states so that it's easy to tell what state you're in and what state you want to go to. Each state may optionally define actions that are triggered upon entering the state, after entering the state, and upon exiting the state. They may also define rules for switching to other states, and these rules may specify the execution of switch-specific actions. All actions are defined in terms of anonymous subroutines that should expect an FSA::State object itself to be passed as the sole argument.

FSA::Rules objects and the FSA::State objects that make them up are all implemented as empty hash references. This design allows the action subroutines to use the FSA::State object passed as the sole argument, as well as the FSA::Rules object available via its machine() method, to stash data for other states to access, without the possibility of interfering with the state or the state machine itself.


To install this module, type the following:

perl Build.PL
./Build test
./Build install

Or, if you don't have Module::Build installed, type the following:

perl Makefile.PL
make test
make install


This module requires no modules or libraries not already included with Perl. It does, however recommend the following modules:

  • GraphViz 2.00
  • Text::Wrap
  • Storable 2.05
  • B::Deparse 0.61

Copyright and License

Copyright (c) 2002-2015, David E. Wheeler. Some Rights Reserved.

This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.