Add contains function

Author: klimick

composer.json

@@ -66,6 +66,7 @@
             "src/Fp/Functions/Collection/FlatMap.php",
             "src/Fp/Functions/Collection/Traverse.php",
             "src/Fp/Functions/Collection/Sequence.php",
+            "src/Fp/Functions/Collection/Contains.php",
             "src/Fp/Functions/Collection/Fold.php",
             "src/Fp/Functions/Collection/Tap.php",
             "src/Fp/Functions/Collection/GroupBy.php",

src/Fp/Functions/Collection/Contains.php

@@ -0,0 +1,35 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Fp\Collection;
+
+/**
+ * Checks if a value exists in an array.
+ *
+ * ```php
+ * >>> contains(42, [40, 41, 42]);
+ * => true
+ * >>> contains(43, [40, 41, 42]);
+ * => false
+ * ```
+ */
+function contains(mixed $elem, iterable $collection): bool
+{
+    /** @var mixed $item */
+    foreach ($collection as $item) {
+        if ($item === $elem) {
+            return true;
+        }
+    }
+
+    return false;
+}
+
+/**
+ * Varargs version of {@see contains()}
+ */
+function containsT(mixed $elem, mixed ...$items): bool
+{
+    return contains($elem, $items);
+}

tests/Runtime/Functions/Collection/ContainsTest.php

@@ -0,0 +1,21 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Runtime\Functions\Collection;
+
+use PHPUnit\Framework\TestCase;
+
+use function Fp\Collection\contains;
+use function Fp\Collection\containsT;
+
+final class ContainsTest extends TestCase
+{
+    public function testContains(): void
+    {
+        $this->assertTrue(contains(42, [40, 41, 42]));
+        $this->assertFalse(contains(43, [40, 41, 42]));
+        $this->assertTrue(containsT(42, 40, 41, 42));
+        $this->assertFalse(containsT(43, 40, 41, 42));
+    }
+}