#Nools

Nools is a rules engine for node based on the rete network.

Installation

npm install nools

#Usage

• Flows * Defining A Flow * Sessions * Facts * Firing * Disposing

• Defining Rules

  • Structure
  • Constraints
  • Actions

• Fibonacci

To get started with nools the examples and tests are a great place to get started.

##Defining a flow

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

###Pragmatically

var nools = require("nools");

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

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

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

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

In the above flow definition 2 rules were defined

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

###Nools DSL

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

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

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

rule Goodbye {
    when {
        m : Message m.message =~ /.*goodbye$/;
    }
    then {
        console.log(m.message);
    }
}

To use the flow

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

##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.

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.

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

To retract 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);

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.message = "hello goodbye";

session.modify(m);

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

modify and retract are typically used during the execution of the rules.

##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);
    }else{
        console.log("done");
    }
})

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

Example of the promise api

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

##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 growing a large memory footprint.

   session.dispose();

#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);
    }
}

###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).

Prgamatically

[
   //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;
}

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 define alias/reference can be used within the pattern. Available operators are.
   • &&, AND, and
   • ||, OR, or
   • >, <, >=, <=, gt, lt, gte, lte
   • ==, !=, =~, eq, neq, like
   • +, -, *, /
   • - (unary minus)
   • . (member operator)
   • in (check inclusion 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.

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

function (facts, engine) {
        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);
    }

If you have an async action that needs to take place an optional third argument can be passed in which is a function to 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 any arguments are passed into next it is assumed there was an error and the session will error out.

To define the action 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.

#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", {priority:1}, [
        ["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]

Fiboncci 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 {
    priority:1,
    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