diff --git a/src/AsString.php b/src/AsString.php
index 16d1890..9c20b6a 100644
--- a/src/AsString.php
+++ b/src/AsString.php
@@ -24,7 +24,7 @@ private function compile(string $value): string
             PHP;
     }
 
-    private function evaluate(array $context, int|float|string $value): string
+    private function evaluate(array $context, float|int|string $value): string
     {
         return (string) $value;
     }
diff --git a/src/DateTime.php b/src/DateTime.php
index bf0f94a..c35d449 100644
--- a/src/DateTime.php
+++ b/src/DateTime.php
@@ -24,7 +24,7 @@ private function compile(string $date, string $format, string $timezone = 'null'
             PHP;
     }
 
-    private function evaluate(array $context, string $date, string $format, string $timezone = null)
+    private function evaluate(array $context, string $date, string $format, ?string $timezone = null)
     {
         return \DateTimeImmutable::createFromFormat($format, $date, null !== $timezone ? new \DateTimeZone($timezone) : null);
     }
diff --git a/src/FileExtension.php b/src/FileExtension.php
new file mode 100644
index 0000000..bc89121
--- /dev/null
+++ b/src/FileExtension.php
@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\StringExpressionLanguage;
+
+use Symfony\Component\ExpressionLanguage\ExpressionFunction;
+
+final class FileExtension extends ExpressionFunction
+{
+    public function __construct($name)
+    {
+        parent::__construct(
+            $name,
+            $this->compile(...)->bindTo($this),
+            $this->evaluate(...)->bindTo($this)
+        );
+    }
+
+    private function compile(string $value): string
+    {
+        return <<<PHP
+            (function () use (\$input) : ?string {
+                \$validExtensions = ['jpg', 'jpeg', 'png', 'gif', 'bmp', 'svg', 'pdf', 'mp4', 'webm', 'mp3'];
+                
+                \$extension = \\pathinfo({$value})['extension'] ?? null;
+                if (!\\in_array(\$extension, \$validExtensions, true)) {
+                    return null;
+                }
+                
+                return \$extension;
+            })()
+            PHP;
+    }
+
+    private function evaluate(array $context, string $file): ?string
+    {
+        $validExtensions = ['jpg', 'jpeg', 'png', 'gif', 'bmp', 'svg'];
+
+        $extension = pathinfo($file)['extension'] ?? null;
+
+        if (!\in_array($extension, $validExtensions, true)) {
+            return null;
+        }
+
+        return $extension;
+    }
+}
diff --git a/src/Now.php b/src/Now.php
index a4d4b15..02951f3 100644
--- a/src/Now.php
+++ b/src/Now.php
@@ -17,14 +17,14 @@ public function __construct($name)
         );
     }
 
-    private function compile(string $timezone = null): string
+    private function compile(?string $timezone = null): string
     {
         return <<<PHP
                 (new \\DateTime('now', {$timezone} !== null ? new \\DateTimeZone({$timezone}) : null))
             PHP;
     }
 
-    private function evaluate(array $context, string $timezone = null)
+    private function evaluate(array $context, ?string $timezone = null)
     {
         return new \DateTime('now', null !== $timezone ? new \DateTimeZone($timezone) : null);
     }
diff --git a/src/Slugify.php b/src/Slugify.php
new file mode 100644
index 0000000..21155e8
--- /dev/null
+++ b/src/Slugify.php
@@ -0,0 +1,55 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Kiboko\Component\StringExpressionLanguage;
+
+use Symfony\Component\ExpressionLanguage\ExpressionFunction;
+
+final class Slugify extends ExpressionFunction
+{
+    public function __construct($name)
+    {
+        parent::__construct(
+            $name,
+            $this->compile(...)->bindTo($this),
+            $this->evaluate(...)->bindTo($this)
+        );
+    }
+
+    private function compile(string $value, string $divider = '-'): string
+    {
+        return <<<PHP
+            (function () use (\$input) : string {
+                \$text = preg_replace('~[^\\pL\\d]+~u', {$divider}, {$value});
+                \$text = iconv('utf-8', 'us-ascii//TRANSLIT', \$text);
+                \$text = preg_replace('~[^-\\w]+~', '', \$text);
+                \$text = trim(\$text, {$divider});
+                \$text = preg_replace('~-+~', {$divider}, \$text);
+                \$text = strtolower(\$text);
+
+                if (strlen(\$text) <= 0) {
+                    return '';
+                }
+
+                return \$text;
+            })()
+            PHP;
+    }
+
+    private function evaluate(array $context, string $value, string $divider = '-'): string
+    {
+        $text = preg_replace('~[^\pL\d]+~u', $divider, $value);
+        $text = iconv('utf-8', 'us-ascii//TRANSLIT', $text);
+        $text = preg_replace('~[^\-\w]+~', '', $text);
+        $text = trim($text, $divider);
+        $text = preg_replace('~-+~', $divider, $text);
+        $text = strtolower($text);
+
+        if (\strlen($text) <= 0) {
+            return 'n-a';
+        }
+
+        return $text;
+    }
+}
diff --git a/src/StringExpressionLanguageProvider.php b/src/StringExpressionLanguageProvider.php
index b0c768b..6d6c390 100644
--- a/src/StringExpressionLanguageProvider.php
+++ b/src/StringExpressionLanguageProvider.php
@@ -37,6 +37,8 @@ public function getFunctions(): array
             new AsFloat('asFloat'),
             new AsInteger('asInteger'),
             new AsString('asString'),
+            new Slugify('slugify'),
+            new FileExtension('fileExtension'),
         ];
     }
 }