Version: 4.0.0-alpha

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");
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