proof of concept

.gitignore

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+# Created by .ignore support plugin (hsz.mobi)
+/.idea/
+
+# PHP
+/vendor/
+/node_modules/
+
+test.*.php

composer.json

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+{
+    "name": "kadet/predicate",
+    "description": "Functional library for PHP",
+    "type": "library",
+    "license": "MIT",
+    "authors": [
+        {
+            "name": "Kacper Donat",
+            "email": "kadet1090@gmail.com"
+        }
+    ],
+    "require": {
+        "php": ">=7.1"
+    },
+    "require-dev": {
+        "phpunit/phpunit": "^7.0"
+    },
+    "autoload": {
+        "psr-4": {
+            "Kadet\\Functional\\": "./src/"
+        },
+        "files": [
+            "./src/functions.php"
+        ]
+    }
+}

src/Predicate.php

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+<?php
+/**
+ * Copyright 2018 Kacper Donat
+ *
+ * @author Kacper "Kadet" Donat <kacper@kadet.net>
+ *
+ * Full license available in separate LICENSE file
+ */
+
+namespace Kadet\Functional;
+
+
+interface Predicate
+{
+    public function __invoke(...$args): bool;
+
+    public function not(): Predicate;
+
+    public function and(...$predicate): Predicate;
+    public function or(...$predicate): Predicate;
+}

src/Predicate/AbstractPredicate.php

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+<?php
+/**
+ * Copyright 2018 Kacper Donat
+ *
+ * @author Kacper "Kadet" Donat <kacper@kadet.net>
+ *
+ * Full license available in separate LICENSE file
+ */
+
+namespace Kadet\Functional\Predicate;
+
+
+use Kadet\Functional\Predicate;
+use function Kadet\Functional\predicate;
+
+abstract class AbstractPredicate implements Predicate
+{
+    public function not(): Predicate
+    {
+        return new NegatedPredicate($this);
+    }
+
+    public function and(...$predicate): Predicate
+    {
+        array_unshift($predicate, $this);
+        return new AllOfPredicate(...array_map(predicate::class, $predicate));
+    }
+
+    public function or(...$predicate): Predicate
+    {
+        array_unshift($predicate, $this);
+        return new AnyOfPredicate(...array_map(predicate::class, $predicate));
+    }
+}

src/Predicate/AllOfPredicate.php

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+<?php
+/**
+ * Copyright 2018 Kacper Donat
+ *
+ * @author Kacper "Kadet" Donat <kacper@kadet.net>
+ *
+ * Full license available in separate LICENSE file
+ */
+
+namespace Kadet\Functional\Predicate;
+
+
+use Kadet\Functional\Predicate;
+
+class AllOfPredicate extends AbstractPredicate
+{
+    /**
+     * Array of predicates to check if all are satisfied.
+     * @var \Kadet\Functional\Predicate[]
+     */
+    private $predicates = [];
+
+    public function __construct(Predicate ...$predicates)
+    {
+        $this->predicates = $predicates;
+    }
+
+    public function and(...$predicate): Predicate
+    {
+        $predicate = array_merge($this->predicates, $predicate);
+        return parent::and($predicate);
+    }
+
+    public function __invoke(...$args): bool
+    {
+        foreach ($this->predicates as $predicate) {
+            if (!$predicate(...$args)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+}

src/Predicate/AnyOfPredicate.php

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+<?php
+/**
+ * Copyright 2018 Kacper Donat
+ *
+ * @author Kacper "Kadet" Donat <kacper@kadet.net>
+ *
+ * Full license available in separate LICENSE file
+ */
+
+namespace Kadet\Functional\Predicate;
+
+
+use Kadet\Functional\Predicate;
+
+class AnyOfPredicate extends AbstractPredicate
+{
+    /**
+     * Array of predicates to check if all are satisfied.
+     * @var \Kadet\Functional\Predicate[]
+     */
+    private $predicates = [];
+
+    public function __construct(Predicate ...$predicates)
+    {
+        $this->predicates = $predicates;
+    }
+
+    public function or(...$predicate): Predicate
+    {
+        $predicate = array_merge($this->predicates, $predicate);
+        return parent::or($predicate);
+    }
+
+
+    public function __invoke(...$args): bool
+    {
+        foreach ($this->predicates as $predicate) {
+            if ($predicate(...$args)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}

src/Predicate/ClosurePredicate.php

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+<?php
+/**
+ * Copyright 2018 Kacper Donat
+ *
+ * @author Kacper "Kadet" Donat <kacper@kadet.net>
+ *
+ * Full license available in separate LICENSE file
+ */
+
+namespace Kadet\Functional\Predicate;
+
+
+class ClosurePredicate extends AbstractPredicate
+{
+    /**
+     * @var \Closure
+     */
+    private $closure;
+
+    /**
+     * ClosurePredicate constructor.
+     *
+     * @param \Closure $closure
+     */
+    public function __construct(\Closure $closure)
+    {
+        $this->closure = $closure;
+    }
+
+    public function __invoke(...$args): bool
+    {
+        return ($this->closure)(...$args);
+    }
+}

src/Predicate/NegatedPredicate.php

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+<?php
+/**
+ * Copyright 2018 Kacper Donat
+ *
+ * @author Kacper "Kadet" Donat <kacper@kadet.net>
+ *
+ * Full license available in separate LICENSE file
+ */
+
+namespace Kadet\Functional\Predicate;
+
+
+use Kadet\Functional\Predicate;
+
+class NegatedPredicate extends AbstractPredicate
+{
+    /**
+     * Predicate to be negated.
+     * @var \Kadet\Functional\Predicate
+     */
+    private $negated;
+
+    public function __construct(Predicate $predicate)
+    {
+        $this->negated = $predicate;
+    }
+
+    public function not(): Predicate
+    {
+        // negation of negations is plain value
+        return $this->negated;
+    }
+
+    public function __invoke(...$args): bool
+    {
+        return !($this->negated)(...$args);
+    }
+}

src/functions.php

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+<?php
+
+namespace Kadet\Functional;
+
+use Kadet\Functional\Predicate\ClosurePredicate;
+
+/**
+ * @param $predicate
+ *
+ * @return \Kadet\Functional\Predicate
+ * @throws \Exception
+ */
+function predicate($predicate): Predicate
+{
+    if ($predicate instanceof Predicate) {
+        return $predicate;
+    }
+
+    if (is_callable($predicate)) {
+        return new ClosurePredicate(\Closure::fromCallable($predicate));
+    }
+
+    // todo better exception
+    throw new \Exception();
+}
+