README

The version of Ruler is forked from bobthecow/Ruler. It removes the ability for a rule to store a callback which can be executed when the rule passes (this should be delegated to another mechanism).

Additionally when a rule does not pass, the reason for the failure is stored.

Ruler is a simple stateless production rules engine for PHP 5.3+.

Ruler has an easy, straightforward DSL

... provided by the RuleBuilder:

<?php

$rb = new RuleBuilder;
$rule = $rb->create(
    $rb->logicalAnd(
        $rb['minNumPeople']->lessThanOrEqualTo($rb['actualNumPeople']),
        $rb['maxNumPeople']->greaterThanOrEqualTo($rb['actualNumPeople'])
    )
);

$context = new Context(array(
    'minNumPeople' => 5,
    'maxNumPeople' => 25,
    'actualNumPeople' => function() {
        return 6;
    },
));

$rule->evaluate($context); // "true"

Of course, if you're not into the whole brevity thing

... you can use it without a RuleBuilder:

<?php

$actualNumPeople = new Variable('actualNumPeople');
$rule = new Rule(
    new Operator\LogicalAnd(array(
        new Operator\LessThanOrEqualTo(new Variable('minNumPeople'), $actualNumPeople),
        new Operator\GreaterThanOrEqualTo(new Variable('maxNumPeople'), $actualNumPeople)
    ))
);

$context = new Context(array(
    'minNumPeople' => 5,
    'maxNumPeople' => 25,
    'actualNumPeople' => function() {
        return 6;
    },
));

$rule->evaluate($context); // "true"

But that doesn't sound too fun, does it?

Things you can do with your Ruler

Compare things

<?php

// These are Variables. They'll be replaced by terminal values during Rule evaluation.

$a = $rb['a'];
$b = $rb['b'];

// Here are bunch of Propositions. They're not too useful by themselves, but they
// are the building blocks of Rules, so you'll need 'em in a bit.

$a->greaterThan($b);          // true if $a > $b
$a->greaterThanOrEqualTo($b); // true if $a >= $b
$a->lessThan($b);             // true if $a < $b
$a->lessThanOrEqualTo($b);    // true if $a <= $b
$a->equalTo($b);              // true if $a == $b
$a->notEqualTo($b);           // true if $a != $b
$a->contains($b);             // true if in_array($b, $a) || strpos($b, $a) !== false
$a->doesNotContain($b);       // true if !in_array($b, $a) || strpos($b, $a) === false
$a->sameAs($b);               // true if $a === $b
$a->notSameAs($b);            // true if $a !== $b

Combine things

<?php

// Create a Rule with an $a == $b condition
$aEqualsB = $rb->create($a->equalTo($b));

// Create another Rule with an $a != $b condition
$aDoesNotEqualB = $rb->create($a->notEqualTo($b));

// Now combine them for a tautology!
// (Because Rules are also Propositions, they can be combined to make MEGARULES)
$eitherOne = $rb->create($rb->logicalOr($aEqualsB, $aDoesNotEqualB));

// Just to mix things up, we'll populate our evaluation context with completely
// random values...
$context = new Context(array(
    'a' => rand(),
    'b' => rand(),
));

// Hint: this is always true!
$eitherOne->evaluate($context);

Combine more things

<?php

$rb->logicalNot($aEqualsB);                  // The same as $aDoesNotEqualB :)
$rb->logicalAnd($aEqualsB, $aDoesNotEqualB); // True if both conditions are true
$rb->logicalOr($aEqualsB, $aDoesNotEqualB);  // True if either condition is true
$rb->logicalXor($aEqualsB, $aDoesNotEqualB); // True if only one condition is true

`evaluate` Rules

evaluate() a Rule with Context to figure out whether it is true.

<?php

$context = new Context(array('userName', function() {
    return isset($_SESSION['userName']) ? $_SESSION['userName'] : null;
}));

$userIsLoggedIn = $rb->create($rb['userName']->notEqualTo(null));

if ($userIsLoggedIn->evaluate($context)) {
    // Do something special for logged in users!
}

Dynamically populate your evaluation Context

Several of our examples above use static values for the context Variables. While that's good for examples, it's not as useful in the Real World. You'll probably want to evaluate Rules based on all sorts of things...

You can think of the Context as a ViewModel for Rule evaluation. You provide the static values, or even code for lazily evaluating the Variables needed by your Rules.

<?php

$context = new Context;

// Some static values...
$context['reallyAnnoyingUsers'] = array('bobthecow', 'jwage');

// You'll remember this one from before
$context['userName'] = function() {
    return isset($_SESSION['userName']) ? $_SESSION['userName'] : null;
};

// Let's pretend you have an EntityManager named `$em`...
$context['user'] = function() use ($em, $context) {
    if ($userName = $context['userName']) {
        return $em->getRepository('Users')->findByUserName($userName);
    }
};

$context['orderCount'] = function() use ($em, $context) {
    if ($user = $context['user']) {
        return $em->getRepository('Orders')->findByUser($user)->count();
    }

    return 0;
};

Now you have all the information you need to make Rules based on Order count or the current User, or any number of other crazy things. I dunno, maybe this is for a shipping price calculator?

If the current User has placed 5 or more orders, but isn't "really annoying", give 'em free shipping.

Access variable properties

As an added bonus, Ruler lets you access properties, methods and offsets on your Context Variable values. This can come in really handy.

Say we wanted to log the current user's name if they are an administrator:

// Reusing our $context from the last example...

// We'll define a few context variables for determining what roles a user has,
// and their full name:

$context['userRoles'] = function() use ($em, $context) {
    if ($user = $context['user']) {
        return $user->roles();
    } else {
        // return a default "anonymous" role if there is no current user
        return array('anonymous');
    }
};

$context['userFullName'] = function() use ($em, $context) {
    if ($user = $context['user']) {
        return $user->fullName;
    }
};


// Now we'll create a rule to write the log message

$rb->create(
    $rb->logicalAnd(
        $userIsLoggedIn,
        $rb['userRoles']->contains('admin')
    ),
    function() use ($context, $logger) {
        $logger->info(sprintf("Admin user %s did a thing!", $context['userFullName']));
    }
);

That was a bit of a mouthful. Instead of creating context Variables for everything we might need to access in a rule, we can use VariableProperties, and their convenient RuleBuilder interface:

// We can skip over the Context Variable building above. We'll simply set our, 
// default roles on the VariableProperty itself, then go right to writing rules:

$rb['user']['roles'] = array('anonymous');

$rb->create(
    $rb->logicalAnd(
        $userIsLoggedIn,
        $rb['user']['roles']->contains('admin')
    ),
    function() use ($context, $logger) {
        $logger->info(sprintf("Admin user %s did a thing!", $context['user']['fullName']);
    }
);

If the parent Variable resolves to an object, and this VariableProperty name is "bar", it will do a prioritized lookup for:

A method named bar
A public property named bar
ArrayAccess + offsetExists named bar

If the Variable resolves to an array it will return:

Array index bar

If none of the above are true, it will return the default value for this VariableProperty.

But that's not all...

Check out the test suite for more examples (and some hot CS 320 combinatorial logic action).

Ruler is plumbing. Bring your own porcelain.

Ruler doesn't bother itself with where Rules come from. Maybe you have a RuleManager wrapped around an ORM or ODM. Perhaps you write a simple DSL and parse static files.

Whatever your flavor, Ruler will handle the logic.

markup / ruler

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