kirouane/logic

PROLOG adaptation

dev-master 2019-06-18 11:42 UTC

Requires (Dev)

• phpro/grumphp: ^0.15.2
• phpstan/phpstan: ^0.11.8
• phpunit/phpunit: ^7.5

MIT

• nassim.kirouane

• php
• logic
• prolog
• logic programming

README

This PHP library is inspired by PROLOG which is a Logic Programming Language. People who are accustomed with PROLOG will find some interesting features.

Install

composer require kirouane/logic

Examples

The examples below are based on this excellent post about PROLOG.

Example 1 : Queries

<?php
use Logic\Facts;
$likes = new Facts();

// fact declaration
$likes->is('alice', 'bob');
$likes->is('bob','carol');
$likes->is('james', 'mary');
$likes->is('mary', 'james');

/* Let's do some queries*/


var_dump($likes('alice', 'bob')->found());
//bool(true) | We found a match in our facts !

var_dump($likes('bob', 'alice')->found());
//bool(false) | Bob doesn't like alice according to our facts

var_dump($likes('mary', 'john')->found());
//bool(false) | Bob doesn't like alice according to our facts

Example 2 : Variables

Now, we want to know who Alice likes. We achieve this by using variables. A variable must start with underscore _ character. Let's see un example.

/* Who does alice like? */
var_dump($likes('alice', '_Who')->toArray());

/*
array(1) {
  [0] =>
  array(1) {
    '_Who' =>
    string(3) "bob"
  }
}
*/

Example 3 : Rules

Let’s write a rule called "love compatible" using the facts we already defined above.

$loveCompatible = new Rule(function($x, $y) use($likes) {
    /** @var RuleRunner $this */
    return $this->andLogic(
        $likes($x, $y),
        $likes($y, $x)
    );
});


/* Now let’s make some queries */

//Is james compatible with someone?
var_dump($loveCompatible('james', '_Who')->toArray());

/*
array(1) {
  [0] =>
  array(1) {
    '_Who' =>
    string(4) "mary"
  }
}
 */

// find all love pairs with the known facts
var_dump($loveCompatible('_X', '_Y')->toArray());

/*
array(2) {
  [0] =>
  array(2) {
    '_X' =>
    string(5) "james"
    '_Y' =>
    string(4) "mary"
  }
  [1] =>
  array(2) {
    '_X' =>
    string(4) "mary"
    '_Y' =>
    string(5) "james"
  }
}
 */

Example 4 : Rules

Let’s take a look at a more complex example.

$mother = new Facts();
$father = new Facts();

$mother->is('alice', 'lea');
$mother->is('john', 'julia');
$mother->is('lea', 'alberta');
$father->is('james', 'alfred');
$father->is('lea', 'john');


$parent = new Rule(function($x, $y) use($mother, $father) {
    return $this->orLogic(
        $mother($x, $y),
        $father($x, $y)
    );
});

$grandParent = new Rule(function($x, $y) use($parent) {
    $z = new Variable();

    return $this->andLogic(
        $parent($x, $z),
        $parent($z, $y)
    );
});


// Who are alice's grandparents
var_dump($grandParent('alice', '_Who')->toArray());

/*
array(2) {
  [0] =>
  array(1) {
    '_Who' =>
    string(7) "alberta"
  }
  [1] =>
  array(1) {
    '_Who' =>
    string(4) "john"
  }
}
*/

More features

• Recursion
• Filtering
• Ability to use native php functions and operators

Upcoming features

• Arrays
• Objects