Nools

Nools is a rete based rules engine written entirely in javascript.

Installation

npm install nools

Or download the source (minified)

Usage

• Flows * Defining A Flow * Sessions * Facts
  • Assert
  • Retract
  • Modify
  • Retrieving Facts * Firing * Disposing * Removing A Flow * Removing All Flows * Checking If A Flow Exists * Agenda Group
  • Focus
  • Auto Focus * Conflict Resolution
• Defining Rules
  • Structure
  • Salience
  • Scope
  • Constraints
    • Custom
    • Not
    • Or
    • From
    • Exists
  • Actions
    • Async Actions
  • Globals
  • Import
• Browser Support
• Fibonacci

Resources

• Nools Google group
• Examples
  • Conways 2D
  • Conways 3D
  • Sudoku
  • Fibonacci
  • Miss Manners
  • Waltz DB
  • Send More Money
  • Diagnosis
• Tests

Defining a flow

When using nools you define a flow which acts as a container for rules that can later be used to get a session

Programmatically

var nools = require("nools");

var Message = function (message) {
    this.text = message;
};

var flow = nools.flow("Hello World", function (flow) {

    //find any message that start with hello
    flow.rule("Hello", [Message, "m", "m.text =~ /^hello\\sworld$/"], function (facts) {
        facts.m.text = facts.m.text + " goodbye";
        this.modify(facts.m);
    });

    //find all messages then end in goodbye
    flow.rule("Goodbye", [Message, "m", "m.text =~ /.*goodbye$/"], function (facts) {
        console.log(facts.m.text);
    });
});

In the above flow definition 2 rules were defined

• Hello
  • Requires a Message
  • The messages's text must match the regular expression /^hello\\sworld$/
  • When matched the message's text is modified and then we let the engine know that we modified the message.
• Goodbye
  • Requires a Message
  • The messages's text must match the regular expression /.*goodbye$/(anything that ends in goodbye)
  • When matched the resulting message is logged.

DSL

You may also use the nools rules language to define your rules.

The following is the equivalent of the rules defined programmatically above.

define Message {
    text : '',
    constructor : function(message){
        this.text = message;
    }
}

//find any message that starts with hello
rule Hello {
    when {
        m : Message m.text =~ /^hello(\s*world)?$/;
    }
    then {
        modify(m, function(){this.text += " goodbye";});
    }
}

//find all messages then end in goodbye
rule Goodbye {
    when {
        m : Message m.text =~ /.*goodbye$/;
    }
    then {
        console.log(m.text);
    }
}

To use the flow

var flow = nools.compile(__dirname + "/helloworld.nools"),
    Message = flow.getDefined("message");

Flow Events

Each flow can have the following events emitted.

• assert (fact) - emitted when facts are asserted
• retract (fact) - emitted when facts are retracted
• modify (fact) - emitted when facts are modified
• fire (name, rule) - emitted when an activation is fired.

session.on("assert", function(fact){
    //fact was asserted
});

session.on("retract", function(fact){
    //fact was retracted
});

session.on("modify", function(fact){
    //fact was modifed
});

session.on("fire", function(name, rule){
    //a rule was fired.
});

nools.compile

The compile method accepts the following parameters

• source|path - The first argument must either be a path that ends in .nools or a string which is the source of the rules that you wish to compile.
• options?
  • name : This is the name of the flow. You can use this name to look up the flow by using nools.getFlow.
  • define : A hash of Classes that should be aviable to the rules that you are compiling.
  • scope: A hash of items that should be available to rules as they run. (i.e. a logger)
• cb? - an options function to invoke when compiling is done.

Example

rule "person name is bob" {
    when {
        p : Person p.name == 'bob';
    }
    then {
        logger.info("Found person with name of bob");
        retract(p);
    }
}

In the above rules file we make use of a Person class and a logger. In order for nools to properly reference the Class and logger you must specify them in your options.

var flow = nools.compile("personFlow.nools", {
    define: {
        //The person class the flow should use
        Person: Person
    },
    scope: {
        //the logger you want your flow to use.
        logger: logger
    }
});

You may also compile source directly.

var noolsSource = "rule 'person name is bob' {"
    + "   when {"
    + "     p : Person p.name == 'bob';"
    + "   }"
    + "   then {"
    + "       logger.info('Found person with name of bob');"
    + "       retract(p);"
    + "   }"
    + "}";

var flow = nools.compile(noolsSource, {
    define: {
        //The person class the flow should use
        Person: Person
    },
    scope: {
        //the logger you want your flow to use.
        logger: logger
    },
    name: 'person name is bob'
});

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();

Working with facts

Facts are items that the rules should try to match.

Assert

To add facts to the session use assert method.

session.assert(new Message("hello"));
session.assert(new Message("hello world"));
session.assert(new Message("goodbye"));

As a convenience any object passed into getSession will also be asserted.

Note assert is typically used pre engine execution and during the execution of the rules.

flow.getSession(new Message("hello"), new Message("hello world"), new Message("goodbye"));

Retract

To remove facts from the session use the retract method.

var m = new Message("hello");

//assert the fact into the engine
session.assert(m);

//remove the fact from the engine
session.retract(m);

Note retract is typically used during the execution of the rules.

Modify

To modify a fact use the modify method.

Note modify will not work with immutable objects (i.e. strings).

var m = new Message("hello");

session.assert(m);

m.text = "hello goodbye";

session.modify(m);

Note modify is typically used during the execution of the rules.

Retrieving Facts

To get a list of facts currently in the session you can use the getFacts() method exposed on a session.

session.assert(1);
session.assert("A");
session.assert("B");
session.assert(2);

session.getFacts(); //[1, "A", "B", 2];

You may also pass in a Type to getFacts which will return facts only of the given type.

session.assert(1);
session.assert("A");
session.assert("B");
session.assert(2);

session.getFacts(Number); //[1, 2];
session.getFacts(String); //["A", "B"];

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);
        }
    );

Disposing of the session

When working with a lot of facts it is wise to call the dispose method which will purge the current session of all facts, this will help prevent the process from growing a large memory footprint.

session.dispose();

Removing a flow

To remove a defined flow from nools use the deleteFlow function.

var myFlow = nools.flow("flow");

nools.deleteFlow("flow"); //returns nools for chaining

nools.getFlow("flow"); //undefined

You may also remove a flow using the FlowContainer object returned from nools.flow;

var myFlow = nools.flow("flow");

nools.deleteFlow(myFlow); //returns nools for chaining

nools.getFlow("flow"); //undefined

Removing All Flows

To remove all flow from nools use the deleteFlows function.

var myFlow = nools.flow("flow");

nools.deleteFlows(); //returns nools for chaining

nools.getFlow("flow"); //undefined

Checking If A Flow Exists

To check if a flow currently is registering with nools use the hasFlow function;

var myFlow = nools.flow("flow");

nools.hasFlow("flow"); //true

Agenda Groups

Agenda groups allow for logical groups of rules within a flow.

The agenda manages a stack of agenda-groups that are currently in focus. The default agenda-group is called main and all rules that do not have an agenda-group specified are placed into the main agenda-group.

As rules are fired and a particular agenda-group runs out of activations then that agenda-group is popped from the internal agenda-group stack and the next one comes into focus. This continues until focus is explicitly called again or the main agenda-group comes into focus.

Note Once an agenda group loses focus it must be re-added to the stack in order for those activations to be focused again.

To add a rule to an agenda-group you can use the agendaGroup option.

this.rule("Hello World", {agendaGroup: "ag1"}, [Message, "m", "m.name == 'hello'"], function (facts) {
    this.modify(facts.m, function () {
        this.name = "goodbye";
    });
});

this.rule("Hello World2", {agendaGroup: "ag2"}, [Message, "m", "m.name == 'hello'"], function (facts) {
    this.modify(facts.m, function () {
        this.name = "goodbye";
    });
});

Or in the dsl

rule "Hello World" {
    agenda-group: "ag1";
    when{
        m : Message m.name === 'hello';
    }
    then{
        modify(m, function(){
            this.name = "goodbye";
        });
    }
}
rule "Hello World 2" {
    agenda-group: "ag2";
    when{
        m : Message m.name === 'goodbye';
    }
    then {
        modify(m, function(){
            m.name = "hello";
        });
    }
}

In the above rules we have defined two agenda-groups called ag1 and ag2

Focus

When running your rules and you want a particular agenda group to run you must call focus on the session of the flow and specify the agenda-group to add to the stack.

//assuming a flow with the rules specified above.
var fired = [];
flow.getSession(new Message("hello"))
    .focus("ag1")
    .on("fire", function (ruleName) {
        fired.push(ruleName);
    })
    .match(function () {
        console.log(fired);  //[ 'Hello World' ]
    });

Or you can add multiple agenda-groups to the focus stack.

var fired1 = [], fired2 = [];
flow
    .getSession(new Message("goodbye"))
    .focus("ag1")
    .focus("ag2")
    .on("fire", function (ruleName) {
        fired1.push(ruleName);
    })
    .match(function () {
        console.log("Example 1", fired1); //[ 'Hello World', 'Hello World2' ]
    });
flow
    .getSession(new Message("hello"))
    .focus("ag2")
    .focus("ag1")
    .on("fire", function (ruleName) {
        fired3.push(ruleName);
    })
    .match(function () {
        console.log("Example 2", fired2); //[ 'Hello World', 'Hello World2' ]
    });

Notice above that the last agenda-group focused is added to the array first.

Auto Focus

Sometimes you may want an agenda-group to auto-focus whenever a certain rule is activated.

this.rule("Bootstrap", [State, "a", "a.name == 'A' && a.state == 'NOT_RUN'"], function (facts) {
    this.modify(facts.a, function () {
        this.state = 'FINISHED';
    });
});

this.rule("A to B",
    [
        [State, "a", "a.name == 'A' && a.state == 'FINISHED'"],
        [State, "b", "b.name == 'B' && b.state == 'NOT_RUN'"]
    ],
    function (facts) {
        this.modify(facts.b, function () {
            this.state = "FINISHED";
        });
    });

this.rule("B to C",
    {agendaGroup: "B to C", autoFocus: true},
    [
        [State, "b", "b.name == 'B' && b.state == 'FINISHED'"],
        [State, "c", "c.name == 'C' && c.state == 'NOT_RUN'"]
    ],
    function (facts) {
        this.modify(facts.c, function () {
            this.state = 'FINISHED';
        });
        this.focus("B to D");
    });

this.rule("B to D",
    {agendaGroup: "B to D"},
    [
        [State, "b", "b.name == 'B' && b.state == 'FINISHED'"],
        [State, "d", "d.name == 'D' && d.state == 'NOT_RUN'"]
    ],
    function (facts) {
        this.modify(facts.d, function () {
        this.state = 'FINISHED';
    });
});

Or using the dsl

rule Bootstrap {
    when{
        a : State a.name == 'A' && a.state == 'NOT_RUN';
    }
    then{
        modify(a, function(){
            this.state = 'FINISHED';
        });
    }
}


rule 'A to B' {
    when{
        a : State a.name == 'A' && a.state == 'FINISHED';
        b : State b.name == 'B' && b.state == 'NOT_RUN';
    }
    then{
        modify(b, function(){
            this.state = 'FINISHED';
        });
    }
}

rule 'B to C' {
    agenda-group: 'B to C';
    auto-focus: true;
    when{
        b: State b.name == 'B' && b.state == 'FINISHED';
        c : State c.name == 'C' && c.state == 'NOT_RUN';
    }
    then{
        modify(c, function(){
            this.state = 'FINISHED';
        });
        focus('B to D')
    }
}

rule 'B to D' {
    agenda-group: 'B to D';
    when{
        b: State b.name == 'B' && b.state == 'FINISHED';
        d : State d.name == 'D' && d.state == 'NOT_RUN';
    }
    then{
        modify(d, function(){
            this.state = 'FINISHED';
        });
    }
}

In the above rules we created a state machine that has a rule with auto-focus set to true.

This allows you to not have to specify focus when running the flow.

var fired = [];
flow
    .getSession(
        new State("A", "NOT_RUN"),
        new State("B", "NOT_RUN"),
        new State("C", "NOT_RUN"),
        new State("D", "NOT_RUN")
    )
    .on("fire", function (name) {
        fired.push(name);
    })
    .match()
    .then(function () {
        console.log(fired); //["Bootstrap", "A to B", "B to C", "B to D"]
    });

Conflict Resolution

When declaring a flow it is defined with a default conflict resolution strategy. A conflict resolution strategy is used to determine which rule to activate when multiple rules are ready to be activated at the same time.

Resolution Strategies

• salience - sort activations on the specified salience. (NOTE The default salience of a rule is 0).
• activationRecency - sort activations on activation recency. This is a LIFO strategy the latest activation takes precedence.
• factRecency - sort activations based on fact recency. Each time a fact is asserted or modified its recency is incremented.
• bucketCounter - sort activations on the internal bucket counter. The bucket counter is incremented after an activation is fired and the internal workingMemory is altered.

The default conflict resolution strategy consists of salience and activationRecency.

###Examples

Example 1

//activation 1
{
    salience: 0,
    activationRecency: 1
}

//activation 2
{
    salience: 0,
    activationRecency: 2
}

In the above example activation 2 would be fired since it is the most recent activation and the rule salience is the same.

Example 2

//activation 1
{
    salience: 1,
    activationRecency: 1
}

//activation 2
{
    salience: 0,
    activationRecency: 2
}

In this example activation 1 would fire because it has a greater salience

###Overidding The Default Strategy

To override the default strategy you can use the conflictResolution method on a flow.

var flow = nools.flow(/**define your flow**/);

flow.conflictResolution(["salience", "factRecency", "activationRecency"]);

The combination of salience, factRecency, and activationRecency would do the following.

1. Check if the salience is the same, if not use the activation with the greatest salience.
2. If salience is the same check if fact recency is the same. The fact recency is determined by looping through the facts in each activation and until two different recencies are found. The activation with the greatest recency takes precendence.
3. If fact recency is the same check the activation recency.

Example 1

//activation 1
{
    salience: 2,
    factRecency: [1,2,3],
    activationRecency: 1
}

//activation 2
{
    salience: 1,
    factRecency: [1,2,4],
    activationRecency: 2
}

In this example activation 1 would fire because it's salience is the greatest.

Example 2

//activation 1
{
    salience: 1,
    factRecency: [1,2,3],
    activationRecency: 1
}

//activation 2
{
    salience: 1,
    factRecency: [1,2,4],
    activationRecency: 2
}

In Example 2 activation 2 would fire because of the third recency entry.

Example 3

//activation 1
{
    salience: 2,
    factRecency: [1,2,3],
    activationRecency: 1
}

//activation 2
{
    salience: 1,
    factRecency: [1,2,3],
    activationRecency: 2
}

In Example 3 activation 2 would fire because salience and factRecency are the same but activation 2's activation recency is greater.

Defining rules

Rule structure

Lets look at the "Calculate" rule in the Fibonacci example

   //flow.rule(type[String|Function], constraints[Array|Array[[]]], action[Function]);
   flow.rule("Calculate", [
         //Type     alias  pattern           store sequence to s1
        [Fibonacci, "f1",  "f1.value != -1", {sequence:"s1"}],
        [Fibonacci, "f2", "f2.value != -1 && f2.sequence == s1 + 1", {sequence:"s2"}],
        [Fibonacci, "f3", "f3.value == -1 && f3.sequence == s2 + 1"],
        [Result, "r"]
    ], function (facts) {
        var f3 = facts.f3, f1 = facts.f1, f2 = facts.f2;
        var v = f3.value = f1.value + facts.f2.value;
        facts.r.result = v;
        this.modify(f3);
        this.retract(f1);
    });

Or using the nools DSL

rule Calculate{
    when {
        f1 : Fibonacci f1.value != -1 {sequence:s1};
        f2 : Fibonacci f2.value != -1 && f2.sequence == s1 + 1 {sequence:s2};
        f3 : Fibonacci f3.value == -1 && f3.sequence == s2 + 1;
    }
    then {
       modify(f3, function(){
            this.value = f1.value + f2.value;
       });
       retract(f1);
    }
}

Salience

Salience is an option that can be specified on a rule giving it a priority and allowing the developer some control over conflict resolution of activations.

this.rule("Hello4", {salience: 7}, [Message, "m", "m.name == 'Hello'"], function (facts) {
});

this.rule("Hello3", {salience: 8}, [Message, "m", "m.name == 'Hello'"], function (facts) {
});

this.rule("Hello2", {salience: 9}, [Message, "m", "m.name == 'Hello'"], function (facts) {
});

this.rule("Hello1", {salience: 10}, [Message, "m", "m.name == 'Hello'"], function (facts) {
});

Or using the DSL

rule Hello4 {
    salience: 7;
    when {
        m: Message m.name == 'hello';
    }
    then {}
}

rule Hello3 {
    salience: 8;
    when {
        m: Message m.name == 'hello';
    }
    then {}
}

rule Hello2 {
    salience: 9;
    when {
        m: Message m.name == 'hello';
    }
    then {}
}

rule Hello1 {
    salience: 10;
    when {
        m: Message m.name == 'hello';
    }
    then {}
}

In the above flow we define four rules each with a different salience, when a single message is asserted they will fire in order of salience (highest to lowest).

var fired = [];
flow1
    .getSession(new Message("Hello"))
    .on("fire", function (name) {
        fired.push(name);
    })
    .match()
    .then(function(){
        console.log(fired); //["Hello1", "Hello2", "Hello3", "Hello4"]
    });

Scope

Scope allows you to access function from within your rules.

If you are using vanilla JS you can use the scope option when defining your rule.

this.rule("hello rule", {scope: {isEqualTo: isEqualTo}},
   [
      ["or",
         [String, "s", "isEqualTo(s, 'hello')"],
         [String, "s", "isEqualTo(s, 'world')"]
      ],
      [Count, "called", null]
   ],
   function (facts) {
      facts.called.called++;
   });

If you are using the dsl.

function matches(str, regex){
    return regex.test(str);
}

rule Hello {
    when {
        m : Message matches(m.text, /^hello\s*world)?$/);
    }
    then {
        modify(m, function(){
            this.text += " goodbye";
        })
    }
}

rule Goodbye {
    when {
        m : Message matches(m.text, /.*goodbye$/);
    }
    then {
    }
}

Or you can pass in a custom function using the scope option in compile.

rule Hello {
    when {
        m : Message doesMatch(m.text, /^hello\sworld$/);
    }
    then {
        modify(m, function(){
            this.text += " goodbye";
        })
    }
}

rule Goodbye {
    when {
        m : Message doesMatch(m.text, /.*goodbye$/);
    }
    then {
    }
}

Provided the doesMatch function in the scope option of compile.

function matches(str, regex) {
   return regex.test(str);
};
var flow = nools.compile(__dirname + "/rules/provided-scope.nools", {scope: {doesMatch: matches}});

Constraints

Constraints define what facts the rule should match. The constraint is a array of either a single constraint (i.e. Bootstrap rule) or an array of constraints(i.e. Calculate).

Programmatically

[
   //Type     alias  pattern           store sequence to s1
  [Fibonacci, "f1", "f1.value != -1", {sequence:"s1"}],
  [Fibonacci, "f2", "f2.value != -1 && f2.sequence == s1 + 1", {sequence:"s2"}],
  [Fibonacci, "f3", "f3.value == -1 && f3.sequence == s2 + 1"],
  [Result, "r"]
]

Using nools DSL

when {
    f1 : Fibonacci f1.value != -1 {sequence:s1};
    f2 : Fibonacci f2.value != -1 && f2.sequence == s1 + 1 {sequence:s2};
    f3 : Fibonacci f3.value == -1 && f3.sequence == s2 + 1;
    r  : Result;
}

1. Type - is the Object type the rule should match. The available types are

   • String - "string", "String", String
   • Number - "number", "Number", Number
   • Boolean - "boolean", "Boolean", Boolean
   • Date - "date", "Date", Date
   • RegExp - "regexp", "RegExp", RegExp
   • Array - "array", "Array", [], Array
   • Object - "object", "Object", "hash", Object
   • Custom - any custom type that you define

2. Alias - the name the object should be represented as.

3. Pattern(optional) - The pattern that should evaluate to a boolean, the alias that was used should be used to reference the object in the pattern. Strings should be in single quotes, regular expressions are allowed. Any previously defined alias/reference can be used within the pattern. Available operators are.

   • &&, AND, and
   • ||, OR, or
   • >, <, >=, <=, gt, lt, gte, lte
   • ==, ===, !=, !==, =~, !=~, eq, seq, neq, sneq, like, notLike
   • +, -, *, /, %
   • - (unary minus)
   • . (member operator)
   • in (check inclusion in an array)
   • notIn (check that something is not in an array)
   • Defined helper functions
     • now - the current date
     • Date(year?, month?, day?, hour?, minute?, second?, ms?) - creates a new Date object
     • lengthOf(arr, length) - checks the length of an array
     • isTrue(something) - check if something === true
     • isFalse(something) - check if something === false
     • isRegExp(something) - check if something is a RegExp
     • isArray(something) - check if something is an Array
     • isNumber(something) - check if something is an Number
     • isHash(something) - check if something is strictly an Object
     • isObject(something) - check if something is any type of Object
     • isDate(something) - check if something is a Date
     • isBoolean(something) - check if something is a Boolean
     • isString(something) - check if something is a String
     • isUndefined(something) - check if something is a undefined
     • isDefined(something) - check if something is Defined
     • isUndefinedOrNull(something) - check if something is a undefined or null
     • isPromiseLike(something) - check if something is a "promise" like (containing then, addCallback, addErrback)
     • isFunction(something) - check if something is a Function
     • isNull(something) - check if something is null
     • isNotNull(something) - check if something is not null
     • dateCmp(dt1, dt2) - compares two dates return 1, -1, or 0
     • (years|months|days|hours|minutes|seconds)(Ago|FromNow)(interval) - adds/subtracts the date unit from the current time

4. Reference(optional) - An object where the keys are properties on the current object, and values are aliases to use. The alias may be used in succeeding patterns.

Custom Constraint

When declaring your rules progrmmatically you can also use a function as a constraint. The function will be called with an object containing each fact that has matched previous constraints.

var HelloFact = declare({
    instance: {
        value: true,
        constructor: function (value) {
            this.value = value;
        }
    }
});

var flow = nools.flow("custom contraint", function (flow) {
    flow.rule("hello rule", [HelloFact, "h", function (facts) {
        return facts.h.value === true;
    }], function (facts) {
        console.log(facts.h.value); //always true
    });
});

var session = flow.getSession();
session.assert(new HelloFact(false));
session.assert(new HelloFact(true));
session.match().then(function(){
    console.log("DONE");
});

Not Constraint

The not constraint allows you to check that particular fact does not exist.

[
    [Number, "n1"],
    ["not", Number, "n2", "n1 > n2"]
]

Or using the DSL.

when {
    n1: Number;
    not(n2: Number n1 > n2);
}

The previous example will check that for all numbers in the workingMemory there is not one that is greater than n1.

Or Constraint

The or constraint can be used to check for the existence of multiple facts.

[
    ["or",
        [String, "s", "s == 'hello'"],
        [String, "s", "s == 'world'"],
        [String, "s", "s == 'hello world'"]
    ]
]

Using the DSL.

when {
    or(
        s : String s == 'hello',
        s : String s == 'world',
        s : String s == 'hello world'
    );
}

The previous example will evaluate to true if you have a string in workingMemory that equals hello, world, or 'hello world.

Or with Not

The or constraint can be combined with a not constraint to allow for the checking of multiple not conditions without the implcit and.

var flow = nools.flow("or condition with not conditions", function (flow) {
        flow.rule("hello rule", [
                ["or",
                    ["not", Number, "n1", "n1 == 1"],
                    ["not", String, "s1", "s1 == 'hello'"],
                    ["not", Date, "d1", "d1.getDate() == now().getDate()"]
                ],
                [Count, "called", null]
            ], function (facts) {
                facts.called.called++;
            });
        });
});

or using the dsl.

rule MultiNotOrRule {
    when {
        or (
            not(n1: Number n1 == 1),
            not(s1: String s1 == 'hello'),
            not(d1: Date d1.getDate() == now().getDate())
        );
        c: Count;
    }
    then{
        c.called++;
    }
}

Note Using the or with a not will cause the activation to fire for each not condition that passes. In the above examples if none of the three facts existed then the rule would fire three times.

From Constraint

The from modifier allows for the checking of facts that are not necessarily in the workingMemory.

The from modifier can be used to access properties on a fact in workingMemory or you can use javascript expressions.

To access properties on a fact you can use the fact name and the property you wish to use as the source for the from source.

[
    [Person, "p"],
    [Address, "a", "a.zipcode == 88847", "from p.address"],
    [String, "first", "first == 'bob'", "from p.firstName"],
    [String, "last", "last == 'yukon'", "from p.lastName"]
]

Or using the DSL.

when {
    p: Person:
    a: Address a.zipcode == 88847 from p.address;
    first: String first == 'bob' from p.firstName;
    last: String last == 'yukon' from p.lastName;
}

The above example will used the address, firstName and lastName from the person fact.

You can also use the from modifier to check facts that create a graph.

For example assume the person object from above has friends that are also of type Person.

[
    [Person, "p"],
    [Person, "friend", "friend.firstName != p.firstName", "from p.friends"],
    [String, "first", "first =~ /^a/", "from friend.firstName"]
]

Or using the DSL.

when {
    p: Person;
    friend: Person friend.firstName != p.firstName from p.friends;
    first: String first =~ /^a/ from friend.firstName;
}

The above example will pull the friend fact from the friends array property on fact p, and first from the friend's firstName.

You could achieve the same thing using the following code if you assert all friends into working memory.

when {
    p: Person;
    friend: Person friend in p.friends && friend.firstName != p.firstName && p.firstName =~ /^a/;
}

To specify the from source as an expression you can do the following.

[
    [Number, "n1", "from [1,2,3,4,5]"]
]

Or using the dsl

{
    n1: Number from [1,2,3,4,5];
}

Using the above syntax you could use from to bootstrap data.

You can also use any function defined in the scope of the rule or flow

flow.rule("my rule", {
    scope: {
        myArr: function(){
            return [1,2,3,4,5];
        }
    },
    [Number, "n1", "from myArr()"],
    function(facts){
        this.assert(facts.n1);
    }
}

Or using the dsl and the scope option.

rule "my rule", {
    when {
        n1: Number from myArr();
    }
    then{
        assert(n1);
    }
}

###Exists Constraint

exists is the logical inversion of a not constraint. It checks for the existence of a fact in memory.

NOTE If there are multiple facts that satisfy the constraint the rule will ONLY be fired once.

[
    ["exists", Number, "n1", "n1 > 1"]
]

Or using the DSL.

when {
    exists(n1: Number n1 > 1);
}

Assuming the above constraint. The following facts would cause the rule to fire once since there is a number that is greater than 1.

session.assert(1);
session.assert(2);
session.assert(3);
session.assert(4);
session.assert(5);

Action

The action is a function that should be fired when all patterns in the rule match. The action is called in the scope of the engine so you can use this to assert, modify, or retract facts. An object containing all facts and references created by the alpha nodes is passed in as the first argument to the action.

So calculate's action modifies f3 by adding the value of f1 and f2 together and modifies f3 and retracts f1.

function (facts) {
        var f3 = facts.f3, f1 = facts.f1, f2 = facts.f2;
        var v = f3.value = f1.value + facts.f2.value;
        facts.r.result = v;
        this.modify(f3);
        this.retract(f1);
    }

The session is also passed in as a second argument so alternatively you could do the following.

function (facts, session) {
        var f3 = facts.f3, f1 = facts.f1, f2 = facts.f2;
        var v = f3.value = f1.value + facts.f2.value;
        facts.r.result = v;
        session.modify(f3);
        session.retract(f1);
    }

To define the actions with the nools DSL

then {
    modify(f3, function(){
        this.value = f1.value + f2.value;
    });
    retract(f1);
}

For rules defined using the rules language nools will automatically determine what parameters need to be passed in based on what is referenced in the action.

Async Actions

If your action is async you can use the third argument which should be called when the action is completed.

function (facts, engine, next) {
        //some async action
        process.nextTick(function(){
            var f3 = facts.f3, f1 = facts.f1, f2 = facts.f2;
            var v = f3.value = f1.value + facts.f2.value;
            facts.r.result = v;
            engine.modify(f3);
            engine.retract(f1);
            next();
        });
    }

If an error occurs you can pass the error as the first argument to next.

then{
   saveToDatabase(user, function(err){
      next(new Error("Something went BOOM!"));
   });
}

If you are using a Promises/A+ compliant library you can just return a promise from your action and nools will wait for the promise to resolve before continuing.

then{
   return saveToDatabase(user); // assume saveToDatabase returns a promise
}

Globals

Globals are accessible through the current working scope of rules defined in a dsl, very similar to using the scope option when compiling.

Note globals are not part of the working memory and therefore are not accessible in the LHS (when) or your rule.

Globals are used like the following:

global PI = Math.PI;
global SOME_STRING = 'some string';
global TRUE = true;
global NUM = 1.23;
global DATE = new Date();

rule "A Rule" {
    when {
    	$obj: Object;
    }
    then{
    	console.log(PI); //Math.PI;
    	console.log(SOME_STRING); //"some string"
    	console.log(TRUE); //true
    	console.log(NUM); //1.23
    	console.log(DATE); //Thu May 23 2013 15:49:22 GMT-0500 (CDT)
    }
}

If you are using nools in node you can also use a require statement.

NOTE require does not currently work for relative paths.

global util = require("util");

rule "A Rule" {
    when {
    	$obj: Object;
    }
    then{
    	util.log("HELLO WORLD");
    }
}

Importing

The import statement allows you to import other nools files into the current one. This can be used to split up logical flows into small reusable groups of rules.

Define our common model to be used across our flows.

//define.nools
define Count{
    constructor: function(){
        this.called = 0;
    }
}

Create a rules file which imports the define.nools to define our Count model.

//orRule.nools

//import define.nools
import("./define.nools");
rule orRule {
    when {
        or(
            s : String s == 'hello',
            s : String s == 'world'
        );
        count : Count;
    }
    then {
        count.called++;
        count.s = s;
    }
}

Same as orRule.nools import our define.nools

//notRule.nools
import("./defines.nools");
rule notRule {
    when {
        not(s : String s == 'hello');
        count : Count
    }
    then {
        count.called++;
    }
}

Now we can use orRule.nools and notRule.nools to compose a new flow that contains define.nools, orRule.nools and notRule.nools.

Note nools will handle duplicate imports, in this case define.nools will only be imported once.

//import
import("./orRules.nools");
import("./notRules.nools");

Emitting custom events.

You may also emit events from your rule actions using the sessions emit function.

then {
    modify(f3, function(){
        this.value = f1.value + f2.value;
    });
    retract(f1);
    emit("my custom event");
}

To listen to the event just use the on method of the session.

var session = flow.getSession();

session.on("my custom event", function(){
    //custom event called.
});

Browser Support

Nools can also be used in the browser. The only difference is that you cannot pass a file location to the compile method instead you must provide the source.

Nools is compatible with amd(requirejs) and can also be used in a standard script tag.

Example 1.

In this example we compile rules definitions inlined in a script tag.

<script type="text/javascript" src="nools.js"></script>
<script type="text/nools" id="simple">
define Message {
    message : "",
    constructor : function (message) {
        this.text = message;
    }
}

rule Hello {
    when {
        m : Message m.text =~ /^hello\sworld$/
    }
    then {
        modify(m, function(){
            this.text += " goodbye";
        });
    }
}

rule Goodbye {
    when {
        m : Message m.text =~ /.*goodbye$/
    }
    then {
        document.getElementById("output").innerHTML += m.text + "</br>";
    }
}
</script>
<script type="text/javascript">
    function init() {
       //get the source
       var source = document.getElementById("simple").innerHTML;
       //compile the source. The name option is required if compiling directly.
       var flow = nools.compile(source, {name: "simple"}),
                Message = flow.getDefined("message"),
                session = flow.getSession();
        //assert your different messages
        session.assert(new Message("goodbye"));
        session.assert(new Message("hello world"));
        session.match();
    }
</script>

Using a compiled dsl.

You may also use the nools executable to compile source into a browser friendly format skipping the need for compiling each time.

nools compile ./my/rules.nools > ./compiled.js

To use the flow require the compile version either through a script tag, amd/requirejs, or commonjs require.

If you import the flow using a script tag you can get a reference to the flow by using nools.getFlow.

nools.getFlow("rules");

You may also specify the name of the flow when compiling, it defaults to the name of the nools file less ".nools"

nools compile -n "my rules" ./my/rules.nools

nools.getFlow("my rules");

If you are using requirejs or nools must be required using something other than require("nools") then you can specify a location of the nools source.

nools compile -nl "./location/to/nools" ./my/rules.nools

RequireJS examples

Examples of using nools with require js are located in the examples directory.

Examples

Fibonacci

"use strict";

var nools = require("nools");

var Fibonacci = function (sequence, value) {
    this.sequence = sequence;
    this.value = value || -1;
};

var Result = function (result) {
    this.result = result || -1;
};


var flow = nools.flow("Fibonacci Flow", function (flow) {

    flow.rule("Recurse", [
        ["not", Fibonacci, "f", "f.sequence == 1"],
        [Fibonacci, "f1", "f1.sequence != 1"]
    ], function (facts) {
        var f2 = new Fibonacci(facts.f1.sequence - 1);
        this.assert(f2);
    });

    flow.rule("Bootstrap", [
          Fibonacci, "f", "f.value == -1 && (f.sequence == 1 || f.sequence == 2)"
    ], function (facts) {
        var f = facts.f;
        f.value = 1;
        this.modify(f);
    });

    flow.rule("Calculate", [
        [Fibonacci, "f1", "f1.value != -1", {sequence:"s1"}],
        [Fibonacci, "f2", "f2.value != -1 && f2.sequence == s1 + 1", {sequence:"s2"}],
        [Fibonacci, "f3", "f3.value == -1 && f3.sequence == s2 + 1"],
        [Result, "r"]
    ], function (facts) {
        var f3 = facts.f3, f1 = facts.f1, f2 = facts.f2;
        var v = f3.value = f1.value + facts.f2.value;
        facts.r.result = v;
        this.modify(f3);
        this.retract(f1);
    });
});

var r1 = new Result(),
    session1 = flow.getSession(new Fibonacci(10), r1),
    s1 = new Date;
session1.match().then(function () {
    console.log("%d [%dms]", r1.result, new Date - s1);
    session1.dispose();
});

var r2 = new Result(),
    session2 = flow.getSession(new Fibonacci(150), r2),
    s2 = new Date;
session2.match().then(function () {
    console.log("%d [%dms]", r2.result, new Date - s2);
    session2.dispose();
});

var r3 = new Result(),
    session3 = flow.getSession(new Fibonacci(1000), r3),
    s3 = new Date;
session3.match().then(function () {
    console.log("%d [%dms]", r3.result, new Date - s3);
    session3.dispose();
});

Output

55 [43ms]
9.969216677189305e+30 [383ms]
4.346655768693743e+208 [3580ms]

Fibonacci with nools DSL

//Define our object classes, you can
//also declare these outside of the nools
//file by passing them into the compile method
define Fibonacci {
    value:-1,
    sequence:null
}
define Result {
    value : -1
}

rule Recurse {
    when {
        //you can use not or or methods in here
        not(f : Fibonacci f.sequence == 1);
        //f1 is how you can reference the fact else where
        f1 : Fibonacci f1.sequence != 1;
    }
    then {
        assert(new Fibonacci({sequence : f1.sequence - 1}));
    }
}

rule Bootstrap {
   when {
       f : Fibonacci f.value == -1 && (f.sequence == 1 || f.sequence == 2);
   }
   then{
       modify(f, function(){
           this.value = 1;
       });
   }
}

rule Calculate {
    when {
        f1 : Fibonacci f1.value != -1 {sequence : s1};
        //here we define constraints along with a hash so you can reference sequence
        //as s2 else where
        f2 : Fibonacci f2.value != -1 && f2.sequence == s1 + 1 {sequence:s2};
        f3 : Fibonacci f3.value == -1 && f3.sequence == s2 + 1;
        r : Result
    }
    then {
        modify(f3, function(){
            this.value = r.result = f1.value + f2.value;
        });
        retract(f1);
    }
}

And to run

var flow = nools.compile(__dirname + "/fibonacci.nools");

var Fibonacci = flow.getDefined("fibonacci"), Result = flow.getDefined("result");
var r1 = new Result(),
    session1 = flow.getSession(new Fibonacci({sequence:10}), r1),
    s1 = +(new Date());
session1.match().then(function () {
    console.log("%d [%dms]", r1.result, +(new Date()) - s1);
    session1.dispose();
});

var r2 = new Result(),
    session2 = flow.getSession(new Fibonacci({sequence:150}), r2),
    s2 = +(new Date());
session2.match().then(function () {
    console.log("%d [%dms]", r2.result, +(new Date()) - s2);
    session2.dispose();
});

var r3 = new Result(),
    session3 = flow.getSession(new Fibonacci({sequence:1000}), r3),
    s3 = +(new Date());
session3.match().then(function () {
    console.log("%d [%dms]", r3.result, +(new Date()) - s3);
    session3.dispose();
});

License

MIT https://github.com/C2FO/nools/raw/master/LICENSE

Meta

• Code: git clone git://github.com/C2FO/nools.git