diff --git a/README.md b/README.md
index 23a60e7..d2372a6 100644
--- a/README.md
+++ b/README.md
@@ -50,7 +50,7 @@ $variables = [
     'show_container' => false,
 ];
 
-// Absolute file path or file content as a string
+// Absolute file path to a text file
 $file_path = __DIR__ . '/hello.html';
 
 $parser = new Parser($file_path, $variables);
@@ -110,7 +110,8 @@ Parsed HTML to a PHP string
 </body>
 </html>
 ```
-## Same example but for WordPress shortcode
+
+### Same example but for WordPress shortcode
 
 ```php
 use Serhii\GoodbyeHtml\Parser;
@@ -127,6 +128,21 @@ function shortcode_callback() {
 }
 ```
 
+## Options
+
+The instance of `Parser` class takes the third argument as a `ParserOption` enum. You can pass it to the constructor of the `Parser` class as a third argument. For now, it has only a single options:
+
+#### `ParserOption::PARSE_TEXT`
+If you pass this option, the parser, instead of getting the content of the provided file path, will parse the provided string. This option is useful when you want to parse a string instead of a file.
+
+```php
+$parser = new Parser('<div>{{ $title }}</div>', [
+    'title' => 'Hello world'
+], ParserOption::PARSE_TEXT);
+
+// output: <div>Hello world</div>
+```
+
 ## Supported types
 
 Types that you can pass to the parser to include them in the `html/text` file. Note that not all PHP types are supported for know. More types will be added in next releases.
@@ -294,7 +310,16 @@ Loop takes 2 integer arguments. The first argument is from what number start loo
 </div>
 ```
 
+#### Assigning statements
+
+You can assign values to variables inside your text files using curly braces. For example if you want to assign value 5 to variable `$a`, you can do it like this `{{ $a = 5 }}`. You can also use prefix operators to change the value of the variable. For example if you want to assign value false to variable `$is_smoking`, you can do it like this `{{ $is_smoking = !true }}`.
+
+```html
+<div>{{ $age = 33 }}</div>
+```
+
 ## Getting started
+
 ```bash
 $ composer require serhii/goodbye-html
 ```
diff --git a/docs/changelog.md b/docs/changelog.md
index b404b4b..5dc665d 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -2,6 +2,15 @@
 
 ----
 
+## v2.7.0 (2023-11-22)
+
+- Added more tests to make sure that everything works as expected
+- Added more info to the `README.md` file
+- Added added assign statement to the BNF grammar
+- Added a third parameter to a `Parser.php` which excepts `ParserOption` ENUM
+
+----
+
 ## v2.6.0 (2023-11-21)
 
 - Added `elseif` statements to a BNF grammar
diff --git a/docs/goodbye-html.bnf b/docs/goodbye-html.bnf
index f9f2286..f91db61 100644
--- a/docs/goodbye-html.bnf
+++ b/docs/goodbye-html.bnf
@@ -5,7 +5,7 @@
     | <expression-statement>
     | <if-statement>
     | <loop-statement>
-    | <block-statement>
+    | <assign-statement>
 
 <digit> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
 
@@ -29,6 +29,8 @@
 
 <html-statement> ::= <string-literal>
 
+<assign-statement> ::= <variable-expression> "=" <expression>
+
 <expression-statement> ::= <expression>
 
 <ternary-expression> ::= <expression> "?" <expression> ":" <expression>
diff --git a/src/Ast/Expressions/PrefixExpression.php b/src/Ast/Expressions/PrefixExpression.php
index 81cc834..bcf1d5f 100644
--- a/src/Ast/Expressions/PrefixExpression.php
+++ b/src/Ast/Expressions/PrefixExpression.php
@@ -8,6 +8,9 @@
 
 readonly class PrefixExpression implements Expression
 {
+    /**
+     * @param non-empty-string $operator
+     */
     public function __construct(
         public Token $token,
         public string $operator,
@@ -20,6 +23,9 @@ public function tokenLiteral(): string
         return $this->token->literal;
     }
 
+    /**
+     * @return non-empty-string
+     */
     public function string(): string
     {
         return sprintf('(%s%s)', $this->operator, $this->right->string());
diff --git a/src/Ast/Literals/NullLiteral.php b/src/Ast/Literals/NullLiteral.php
index 730bfde..3b77189 100644
--- a/src/Ast/Literals/NullLiteral.php
+++ b/src/Ast/Literals/NullLiteral.php
@@ -20,6 +20,6 @@ public function tokenLiteral(): string
 
     public function string(): string
     {
-        return '';
+        return 'null';
     }
 }
diff --git a/src/CoreParser/CoreParser.php b/src/CoreParser/CoreParser.php
index 736317f..0bef9db 100644
--- a/src/CoreParser/CoreParser.php
+++ b/src/CoreParser/CoreParser.php
@@ -310,6 +310,10 @@ private function parsePrefixExpression(): Expression
 
         $right = $this->parseExpression(Precedence::PREFIX);
 
+        if ($operator === '') {
+            throw new CoreParserException(ParserError::prefixOperatorNotFound());
+        }
+
         return new PrefixExpression($token, $operator, $right);
     }
 
diff --git a/src/CoreParser/ParserError.php b/src/CoreParser/ParserError.php
index a2d6779..f02b7e9 100644
--- a/src/CoreParser/ParserError.php
+++ b/src/CoreParser/ParserError.php
@@ -11,6 +11,9 @@ abstract class ParserError
 {
     private const PREFIX = '[PARSER_ERROR]:';
 
+    /**
+     * @return non-empty-string
+     */
     public static function noPrefixParseFunction(Token $token): string
     {
         return sprintf(
@@ -20,6 +23,9 @@ public static function noPrefixParseFunction(Token $token): string
         );
     }
 
+    /**
+     * @return non-empty-string
+     */
     public static function expectNextTokenToBeDifferent(TokenType $token, Token $peek): string
     {
         return sprintf(
@@ -30,6 +36,9 @@ public static function expectNextTokenToBeDifferent(TokenType $token, Token $pee
         );
     }
 
+    /**
+     * @return non-empty-string
+     */
     public static function elseIfBlockWrongPlace(): string
     {
         return sprintf(
@@ -37,4 +46,12 @@ public static function elseIfBlockWrongPlace(): string
             self::PREFIX,
         );
     }
+
+    /**
+     * @return non-empty-string
+     */
+    public static function prefixOperatorNotFound(): string
+    {
+        return sprintf('%s prefix operator not found', self::PREFIX);
+    }
 }
diff --git a/src/Exceptions/CoreParserException.php b/src/Exceptions/CoreParserException.php
index 639a8be..7effdca 100644
--- a/src/Exceptions/CoreParserException.php
+++ b/src/Exceptions/CoreParserException.php
@@ -8,4 +8,11 @@
 
 class CoreParserException extends Exception
 {
+    /**
+     * @param non-empty-string $message
+     */
+    public function __construct(string $message)
+    {
+        parent::__construct($message);
+    }
 }
diff --git a/src/Exceptions/EvaluatorException.php b/src/Exceptions/EvaluatorException.php
index bbf793f..71f8352 100644
--- a/src/Exceptions/EvaluatorException.php
+++ b/src/Exceptions/EvaluatorException.php
@@ -8,4 +8,11 @@
 
 class EvaluatorException extends Exception
 {
+    /**
+     * @param non-empty-string $message
+     */
+    public function __construct(string $message)
+    {
+        parent::__construct($message);
+    }
 }
diff --git a/src/Exceptions/ParserException.php b/src/Exceptions/ParserException.php
index 3a830d8..f2cd831 100644
--- a/src/Exceptions/ParserException.php
+++ b/src/Exceptions/ParserException.php
@@ -8,4 +8,11 @@
 
 class ParserException extends Exception
 {
+    /**
+     * @param non-empty-string $message
+     */
+    public function __construct(string $message)
+    {
+        parent::__construct($message);
+    }
 }
diff --git a/src/Lexer/Lexer.php b/src/Lexer/Lexer.php
index 2d78cb8..c73edd8 100644
--- a/src/Lexer/Lexer.php
+++ b/src/Lexer/Lexer.php
@@ -11,10 +11,30 @@ class Lexer
 {
     private const LAST_CHAR = 'ø';
 
-    private readonly string $input;
+    /**
+     * The position of the current character in the input (points to current char)
+     *
+     * @var int<0, max>
+     */
     private int $position = 0;
+
+    /**
+     * The position of the next character in the input (points to next char)
+     *
+     * @var int<0, max>
+     */
     private int $nextPosition = 0;
+
+    private readonly string $input;
+
+    /**
+     * The current character under examination
+     */
     private string $char = '';
+
+    /**
+     * Tells us whether we are in HTML or in embedded code
+     */
     private bool $isHtml = true;
 
     public function __construct(string $input)
@@ -74,7 +94,7 @@ private function readEmbeddedCodeToken(): Token
         }
 
         if ($this->isVariableStart()) {
-            $this->advanceChar();
+            $this->advanceChar(); // skip "$"
             return new Token(TokenType::VAR, $this->readIdentifier());
         }
 
@@ -147,12 +167,16 @@ private function advanceChar(): void
         ++$this->nextPosition;
     }
 
+    /**
+     * @return non-empty-string
+     */
     private function peekChar(): string
     {
         if ($this->nextPosition >= strlen($this->input)) {
             return self::LAST_CHAR;
         }
 
+        /** @var non-empty-string */
         return $this->input[$this->nextPosition];
     }
 
@@ -184,6 +208,9 @@ private function isNumber(string $number): bool
         return preg_match('/[0-9.]/', $number) === 1;
     }
 
+    /**
+     * @return non-empty-string
+     */
     private function readIdentifier(): string
     {
         $position = $this->position;
@@ -192,6 +219,7 @@ private function readIdentifier(): string
             $this->advanceChar();
         }
 
+        /** @var non-empty-string $result */
         $result = substr($this->input, $position, $this->position - $position);
 
         // Handle case when identifier is "else if"
@@ -206,6 +234,9 @@ private function readIdentifier(): string
         return $result;
     }
 
+    /**
+     * @return non-empty-string
+     */
     private function readNumber(): string
     {
         $position = $this->position;
@@ -214,6 +245,7 @@ private function readNumber(): string
             $this->advanceChar();
         }
 
+        /** @var non-empty-string */
         return substr($this->input, $position, $this->position - $position);
     }
 
diff --git a/src/Obj/ErrorObj.php b/src/Obj/ErrorObj.php
index 0b2069b..9208279 100644
--- a/src/Obj/ErrorObj.php
+++ b/src/Obj/ErrorObj.php
@@ -6,6 +6,9 @@
 
 readonly class ErrorObj extends Obj
 {
+    /**
+     * @param non-empty-string $message
+     */
     public function __construct(public string $message)
     {
     }
@@ -15,6 +18,9 @@ public function type(): ObjType
         return ObjType::ERROR_OBJ;
     }
 
+    /**
+     * @return non-empty-string
+     */
     public function value(): string
     {
         return $this->message;
diff --git a/src/Parser.php b/src/Parser.php
index aeadc37..a879141 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -24,12 +24,14 @@ class Parser
     private string $html_content;
 
     /**
-     * @param string $file_path Absolute file path or the file content itself
-     * @param array<string, mixed>|null $variables Associative array ['var_name' => 'will be inserted']
+     * @param string $file_path Absolute file path
+     * @param array<non-empty-string, int|string|bool|float|null>|null $variables
+     * @param ParserOption|null $options
      */
     public function __construct(
         private readonly string $file_path,
         private readonly array|null $variables = null,
+        private readonly ParserOption|null $options = null,
     ) {
         $this->html_content = '';
     }
@@ -45,6 +47,10 @@ public function __construct(
      */
     public function parseHtml(): string
     {
+        if ($this->file_path === '') {
+            return '';
+        }
+
         $this->setHtmlContent();
 
         if (!$this->hasVariables()) {
@@ -69,7 +75,7 @@ public function parseHtml(): string
      */
     private function setHtmlContent(): void
     {
-        if (!str_starts_with($this->file_path, '/')) {
+        if ($this->options && $this->options === ParserOption::PARSE_TEXT) {
             $this->html_content = $this->file_path;
             return;
         }
diff --git a/src/ParserOption.php b/src/ParserOption.php
new file mode 100644
index 0000000..87f6ff0
--- /dev/null
+++ b/src/ParserOption.php
@@ -0,0 +1,10 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Serhii\GoodbyeHtml;
+
+enum ParserOption
+{
+    case PARSE_TEXT;
+}
diff --git a/tests/EvaluatorTest.php b/tests/EvaluatorTest.php
index ef2752a..93e2762 100644
--- a/tests/EvaluatorTest.php
+++ b/tests/EvaluatorTest.php
@@ -75,6 +75,8 @@ public static function providerForTestEvalFloatExpression(): array
             ['{{ 3.425 }}', '3.425'],
             ['{{ 1.9 }}', '1.9'],
             ['{{ -3.34 }}', '-3.34'],
+            ['{{ !5.5 }}', ''],
+            ['{{ !0.0 }}', '1'],
         ];
     }
 
@@ -97,6 +99,10 @@ public static function providerForTestEvalBooleanExpression(): array
             ['{{ false }}', ''], // in PHP false to string is ''
             ['{{ !true }}', ''],
             ['{{ !false }}', '1'],
+            ['{{ !!true }}', '1'],
+            ['{{ !!false }}', ''],
+            ['{{ !!!true }}', ''],
+            ['{{ !!!false }}', '1'],
         ];
     }
 
@@ -377,7 +383,9 @@ public static function providerForTestAssignStatement(): array
             ['{{ $his_age = 33 }}<h1>{{ $his_age }}</h1>', '<h1>33</h1>'],
             ['{{ $lang = "PHP" }}{{ $lang="Go" }}{{ $lang }}', 'Go'], // test overriding
             ['{{ if true }}{{ $platform = "Mac" }}{{ $platform }}{{ end }}', 'Mac'],
-            ['{{ $platform = "Linux" }}{{ if true }}{{ $platform }}{{ end }}', 'Linux'],
+            ['{{ $platform = "Linux" . " platform" }}{{ if true }}{{ $platform }}{{ end }}', 'Linux platform'],
+            ['{{ $sum = 22 + 8 }}{{ $sum }}', '30'],
+            ['{{ $isGood = !true }}{{ $isGood ? "Good" : "Bad" }}', 'Bad'],
         ];
     }
 
@@ -400,6 +408,15 @@ public static function providerForTestVariableIsUndefinedOutOfScopes(): array
             ['{{ if false }}{{ else }}{{ $age = 33 }}{{ end }}{{ $age }}', 'age'],
             ['{{ loop 0, 1 }}{{ $index }}{{ end }}{{ $index }}', 'index'],
             ['{{ loop -1, 3 }}{{ $age = 33 }}{{ end }}{{ $age }}', 'age'],
+            [
+                <<<HTML
+                {{ if true }}
+                    {{ if true }} {{ \$var = 3 }} {{ end }}
+                    {{ \$var }}
+                {{ end }}
+                HTML,
+                'var'
+            ],
         ];
     }
 }
diff --git a/tests/ParserTest.php b/tests/ParserTest.php
index 46f1648..8c7e5de 100644
--- a/tests/ParserTest.php
+++ b/tests/ParserTest.php
@@ -55,8 +55,14 @@ public function testParserCanParseTextDirectly(): void
             'cats' => null,
             'name' => 'Elliot',
             'movie' => 'Mr. Robot',
-        ]);
+        ], ParserOption::PARSE_TEXT);
 
         $this->assertSame($expect, $parser->parseHtml());
     }
+
+    public function testParserReturnsEmptyStringWithEmptyFilePath(): void
+    {
+        $parser = new Parser('');
+        $this->assertEmpty($parser->parseHtml());
+    }
 }