NAME
    VS::RuleEngine - Generic rule based processing engine

SYNOPSIS
    A simple example which just randomizes a number 10 times and outputs it
    to screen if it was under 500.

      use VS::RuleEngine::Constants;
      use VS::RuleEngine::Declare;
      
  my $i = 0;
      
  my $engine = engine {
          prehook "check_i" => does {
              $i++;
              
          return KV_ABORT if $i == 10;
              return KV_CONTINUE;
          };
          
      input "random" => does {
              return int(rand(1000));
          };
          
      rule "under_500" => does {
              my $input = $_[KV_INPUT];
              return KV_MATCH if $input->get("random") < 500;
              return KV_NO_MATCH;
          };
          
      action "mark_under_500" => does {
              my ($input, $local) = @_[KV_INPUT, KV_LOCAL];
              $local->set("output" => $input->get("random") . " was under 500");
          };

          run "mark_under_500" => when "under_500";
          
      output "print" => does {
              my $local = $_[KV_LOCAL];
              my $output = $local->get("output");
              print $output, "\n" if defined $output;
          };
      }

    A fictional spam filter

      use VS::RuleEngine::Constants;
      use VS::RuleEngine::Declare;
      
  my $engine = engine {
          prehook "has_more_email" => instanceof "MyApp::HasMoreEmails";
          
      # Returns an Email::Simple instance
          input "email" => instanceof "MyApp::GetEmail";
          
      input "from" => does {
                my $input = $_[KV_INPUT];
                return $input->get("email")->header("From");
          };
          
      rule "is_spam" => instanceof "MyApp::SpamDetector";
          
      rule "is_from_boss" => does {
              my $input = $_[KV_INPUT];
              
          if ($input->get("from") =~ /theboss@company\.com/) {
                  return KV_MATCH;
              }
              
          return KV_NO_MATCH;
          };
          
      action "mark_for_deletion" => does {
              my $local = $_[KV_LOCAL];
              $local->set("delete-email" => 1);
          };
          
      run "mark_for_deletion" => when qw(is_spam is_from_boss);
          
      posthook "process_mail" => does {
              my ($input, $local) = @_[KV_INPUT, KV_LOCAL];
              
          if ($local->get("delete-mail") == 1) {
                  MyApp::EmailHandler->delete($input->get("email"));
              }
              
          return KV_CONTINUE;
          };
      };
      
  $engine->run();

DESCRIPTION
    VS::RuleEngine is a generic rule based processing engine. Processing is
    done while neither any pre nor post iteration hook aborts processing.
    Each engine supports multiple pre- and posthooks, inputs, output,
    actions and rules. An action is attached to one or several rules and is
    executed if any of the rules matches. Input is processed when needed and
    only once per iteration.

    Multiple engines can be run in parallel in a runloop. Runloops can be
    ran until no more data is available for processing or by a single step
    at a time. This way multiple runloops may be executed simultaneously.

USAGE
    VS::RuleEngine has a declarative interface via VS::RuleEngine::Declare
    which is the simplest way to define engines. The synopsis shows an
    exmaple that could be implemented (with reservations for syntax errors).

  Declarative interface
    VS::RuleEngine::Declare

  Loading engines from other sources
    Currently creation of engines are only possible using either the
    declarative interface or by creating "VS::RuleEngine::Engine"-objects
    directly. Future releases will allow loading of engine declarations via
    XML and other formats.

  Runloops
    Runloops transforms engines into something executable and runs them.

    VS::RuleEngine::Runloop

  Inputs, Outputs, Rules, Hooks, Actions
    The components that makes up an engine.

    VS::RuleEngine::Input, VS::RuleEngine::Output, VS::RuleEngine::Rule,
    VS::RuleEngine::Hook, VS::RuleEngine::Action

BUGS AND LIMITATIONS
    Please report any bugs or feature requests to
    "bug-vs-ruleengine@rt.cpan.org", or through the web interface at
    <http://rt.cpan.org>.

AUTHOR
    Claes Jakobsson "<claesjac@cpan.org>"

LICENCE AND COPYRIGHT
    Copyright (c) 2007 - 2008, Versed Solutions "<info@versed.se>". All
    rights reserved.

    This software is released under the MIT license cited below.

  The "MIT" License
    Permission is hereby granted, free of charge, to any person obtaining a
    copy of this software and associated documentation files (the
    "Software"), to deal in the Software without restriction, including
    without limitation the rights to use, copy, modify, merge, publish,
    distribute, sublicense, and/or sell copies of the Software, and to
    permit persons to whom the Software is furnished to do so, subject to
    the following conditions:

    The above copyright notice and this permission notice shall be included
    in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
    OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
    MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
    IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
    CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
    TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
    SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.