Version: 4.0.0-alpha

Working with a session

A session is an instance of the flow that contains a working memory and handles the assertion, modification, and retraction of facts from the engine.

To obtain an engine session from the flow invoke the getSession method.

var session = flow.getSession();

Firing the rules

When you get a session from a flow no rules will be fired until the match method is called.

var session = flow.getSession();
//assert your different messages
session.assert(new Message("goodbye"));
session.assert(new Message("hello"));
session.assert(new Message("hello world"));

//now fire the rules
session.match(function(err){
    if(err){
        console.error(err.stack);
    }else{
        console.log("done");
    }
})

The match method also returns a promise that is resolved once there are no more rules to activate.

session.match().then(
  function(){
      console.log("Done");
  },
  function(err){
    //uh oh an error occurred
    console.error(err.stack);
  });

Fire until halt

You may also run the engine an a "reactive" mode which will continue to match until halt is invoked.

In the following example the rules engine continues to evaluate until the counter reaches 10000. If you remove the "counted to high" rule then the engine would run indefinitely.

define Counter {
    count: 0,
    constructor: function(count){
        this.count = count;
    }
}

//We reached our goal
rule "I can count!" {
    when {
        $ctr: Counter $ctr.count == 10000;
    }
    then{
        console.log("Look ma! I counted to " + $ctr.count);
        halt();
    }
}

//no counter was asserted so create one
rule "not count" {
    when {
        not($ctr: Counter);
    }
    then{
        console.log("Imma gonna count!");
        assert(new Counter(1));
    }
}

//A little status update
rule "give them an update" {
    when{
        $ctr: Counter $ctr.count % 1000 == 0 {count: $count}
    }
    then{
        console.log("Imma countin...");
        modify($ctr, function(){this.count = $count + 1;});
    }
}

//just counting away
rule count {
    when{
        $ctr: Counter {count: $count}
    }
    then{
        modify($ctr, function(){
          this.count = $count + 1;
        });
    }
}

flow.getSession().matchUntilHalt(function(err){
    if(err){
        console.log(err.stack);
        return;
    }
    //halt finally invoked
});

matchUntilHalt also returns a promise.

flow.getSession().matchUntilHalt()
    .then(
        function(){
            //all done!
        },
        function(err){
            console.log(err.stack);
        }
    );

Firing the rules#

Fire until halt#

Firing the rules

Fire until halt