diff --git a/Bin/Pp.php b/Bin/Pp.php
index 9e6a5954..ecfd3b0f 100644
--- a/Bin/Pp.php
+++ b/Bin/Pp.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -45,9 +47,6 @@
  * Class Hoa\Compiler\Bin\Pp.
  *
  * Play with PP.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Pp extends Console\Dispatcher\Kit
 {
@@ -69,8 +68,6 @@ class Pp extends Console\Dispatcher\Kit
 
     /**
      * The entry method.
-     *
-     * @return  int
      */
     public function main()
     {
@@ -163,9 +160,6 @@ public function main()
 
     /**
      * Print trace.
-     *
-     * @param   \Hoa\Compiler\Llk\Parser  $compiler    Compiler.
-     * @return  void
      */
     protected function printTrace(Compiler\Llk\Parser $compiler)
     {
@@ -200,12 +194,8 @@ protected function printTrace(Compiler\Llk\Parser $compiler)
 
     /**
      * Print token sequence.
-     *
-     * @param   \Hoa\Compiler\Llk\Parser  $compiler    Compiler.
-     * @param   string                    $data        Data to lex.
-     * @return  void
      */
-    protected function printTokenSequence(Compiler\Llk\Parser $compiler, $data)
+    protected function printTokenSequence(Compiler\Llk\Parser $compiler, string $data)
     {
         $lexer    = new Compiler\Llk\Lexer();
         $sequence = $lexer->lexMe($data, $compiler->getTokens());
@@ -244,8 +234,6 @@ protected function printTokenSequence(Compiler\Llk\Parser $compiler, $data)
 
     /**
      * The command usage.
-     *
-     * @return  int
      */
     public function usage()
     {
diff --git a/Exception/Exception.php b/Source/Exception/Exception.php
similarity index 92%
rename from Exception/Exception.php
rename to Source/Exception/Exception.php
index 900a3fc9..2cfe4aa5 100644
--- a/Exception/Exception.php
+++ b/Source/Exception/Exception.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -43,9 +45,6 @@
  * Class \Hoa\Compiler\Exception.
  *
  * Extending the \Hoa\Exception\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Exception extends HoaException
 {
@@ -54,4 +53,4 @@ class Exception extends HoaException
 /**
  * Flex entity.
  */
-Consistency::flexEntity('Hoa\Compiler\Exception\Exception');
+Consistency::flexEntity(Exception::class);
diff --git a/Exception/FinalStateHasNotBeenReached.php b/Source/Exception/FinalStateHasNotBeenReached.php
similarity index 95%
rename from Exception/FinalStateHasNotBeenReached.php
rename to Source/Exception/FinalStateHasNotBeenReached.php
index 27a59d79..b6a54554 100644
--- a/Exception/FinalStateHasNotBeenReached.php
+++ b/Source/Exception/FinalStateHasNotBeenReached.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Exception\FinalStateHasNotBeenReached.
  *
  * Extending the \Hoa\Compiler\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class FinalStateHasNotBeenReached extends Exception
 {
diff --git a/Exception/IllegalToken.php b/Source/Exception/IllegalToken.php
similarity index 82%
rename from Exception/IllegalToken.php
rename to Source/Exception/IllegalToken.php
index cb703339..2f52a345 100644
--- a/Exception/IllegalToken.php
+++ b/Source/Exception/IllegalToken.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Exception\IllegalToken.
  *
  * Extending the \Hoa\Compiler\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class IllegalToken extends Exception
 {
@@ -57,14 +56,8 @@ class IllegalToken extends Exception
 
     /**
      * Override line and add column support.
-     *
-     * @param   string  $message    Formatted message.
-     * @param   int     $code       Code (the ID).
-     * @param   array   $arg        RaiseError string arguments.
-     * @param   int     $line       Line.
-     * @param   int     $column     Column.
      */
-    public function __construct($message, $code, $arg, $line, $column)
+    public function __construct(string $message, int $code, $arg, int $line, int $column)
     {
         parent::__construct($message, $code, $arg);
 
@@ -76,10 +69,8 @@ public function __construct($message, $code, $arg, $line, $column)
 
     /**
      * Get column.
-     *
-     * @return  int
      */
-    public function getColumn()
+    public function getColumn(): int
     {
         return $this->column;
     }
diff --git a/Exception/Lexer.php b/Source/Exception/Lexer.php
similarity index 95%
rename from Exception/Lexer.php
rename to Source/Exception/Lexer.php
index ea1d01f8..1eaa8526 100644
--- a/Exception/Lexer.php
+++ b/Source/Exception/Lexer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Exception\Lexer.
  *
  * Extending the \Hoa\Compiler\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Lexer extends Exception
 {
diff --git a/Exception/Rule.php b/Source/Exception/Rule.php
similarity index 95%
rename from Exception/Rule.php
rename to Source/Exception/Rule.php
index edf31c47..f3292816 100644
--- a/Exception/Rule.php
+++ b/Source/Exception/Rule.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Exception\FinalStateHasNotBeenReached.
  *
  * Extending the \Hoa\Compiler\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Rule extends Exception
 {
diff --git a/Exception/UnexpectedToken.php b/Source/Exception/UnexpectedToken.php
similarity index 95%
rename from Exception/UnexpectedToken.php
rename to Source/Exception/UnexpectedToken.php
index 6c22f1f2..9f5a9a28 100644
--- a/Exception/UnexpectedToken.php
+++ b/Source/Exception/UnexpectedToken.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Exception\UnexpectedToken.
  *
  * Extending the \Hoa\Compiler\Exception\UnrecognizedToken class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class UnexpectedToken extends UnrecognizedToken
 {
diff --git a/Exception/UnrecognizedToken.php b/Source/Exception/UnrecognizedToken.php
similarity index 82%
rename from Exception/UnrecognizedToken.php
rename to Source/Exception/UnrecognizedToken.php
index 59963c07..cd668fba 100644
--- a/Exception/UnrecognizedToken.php
+++ b/Source/Exception/UnrecognizedToken.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Exception\UnrecognizedToken.
  *
  * Extending the \Hoa\Compiler\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class UnrecognizedToken extends Exception
 {
@@ -57,14 +56,8 @@ class UnrecognizedToken extends Exception
 
     /**
      * Override line and add column support.
-     *
-     * @param   string  $message    Formatted message.
-     * @param   int     $code       Code (the ID).
-     * @param   array   $arg        RaiseError string arguments.
-     * @param   int     $line       Line.
-     * @param   int     $column     Column.
      */
-    public function __construct($message, $code, $arg, $line, $column)
+    public function __construct(string $message, int $code, $arg, int $line, int $column)
     {
         parent::__construct($message, $code, $arg);
 
@@ -76,10 +69,8 @@ public function __construct($message, $code, $arg, $line, $column)
 
     /**
      * Get column.
-     *
-     * @return  int
      */
-    public function getColumn()
+    public function getColumn(): int
     {
         return $this->column;
     }
diff --git a/Ll1.php b/Source/Ll1.php
similarity index 90%
rename from Ll1.php
rename to Source/Ll1.php
index 53c2cc98..36b846ca 100644
--- a/Ll1.php
+++ b/Source/Ll1.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -46,9 +48,6 @@
  * Class \Hoa\Compiler\Ll1.
  *
  * Provide an abstract LL(1) compiler, based on sub-automata and stacks.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 abstract class Ll1
 {
@@ -322,14 +321,6 @@ abstract class Ll1
 
     /**
      * Singleton, and set parameters.
-     *
-     * @param   array   $skip           Skip.
-     * @param   array   $tokens         Tokens.
-     * @param   array   $states         States.
-     * @param   array   $terminal       Terminal states.
-     * @param   array   $transitions    Transitions table.
-     * @param   array   $actions        Actions table.
-     * @param   array   $names          Names of automata.
      */
     public function __construct(
         array $skip,
@@ -353,13 +344,8 @@ public function __construct(
 
     /**
      * Compile a source code.
-     *
-     * @param   string  $in    Source code.
-     * @return  void
-     * @throws  \Hoa\Compiler\Exception\FinalStateHasNotBeenReached
-     * @throws  \Hoa\Compiler\Exception\IllegalToken
      */
-    public function compile($in)
+    public function compile(string $in)
     {
         $cacheId = md5($in);
 
@@ -653,17 +639,11 @@ public function compile($in)
     /**
      * Consume actions.
      * Please, see the actions table definition to learn more.
-     *
-     * @param   int  $action    Action.
-     * @return  void
      */
-    abstract protected function consume($action);
+    abstract protected function consume(int $action);
 
     /**
      * Compute source code before compiling it.
-     *
-     * @param   string  &$in    Source code.
-     * @return  void
      */
     protected function pre(&$in)
     {
@@ -672,28 +652,21 @@ protected function pre(&$in)
 
     /**
      * Verify compiler state when ending the source code.
-     *
-     * @return  bool
      */
-    protected function end()
+    protected function end(): bool
     {
         return true;
     }
 
     /**
      * Get the result of the compiling.
-     *
-     * @return  mixed
      */
     abstract public function getResult();
 
     /**
      * Set initial line.
-     *
-     * @param   int     $line    Initial line.
-     * @return  int
      */
-    public function setInitialLine($line)
+    public function setInitialLine(int $line): int
     {
         $old                = $this->_initialLine;
         $this->_initialLine = $line;
@@ -703,11 +676,8 @@ public function setInitialLine($line)
 
     /**
      * Set tokens to skip.
-     *
-     * @param   array   $skip    Skip.
-     * @return  array
      */
-    public function setSkip(array $skip)
+    public function setSkip(array $skip): array
     {
         $old         = $this->_skip;
         $this->_skip = $skip;
@@ -718,11 +688,8 @@ public function setSkip(array $skip)
 
     /**
      * Set tokens.
-     *
-     * @param   array   $tokens    Tokens.
-     * @return  array
      */
-    public function setTokens(array $tokens)
+    public function setTokens(array $tokens): array
     {
         $old           = $this->_tokens;
         $this->_tokens = $tokens;
@@ -732,11 +699,8 @@ public function setTokens(array $tokens)
 
     /**
      * Set states.
-     *
-     * @param   array   $states    States.
-     * @return  array
      */
-    public function setStates(array $states)
+    public function setStates(array $states): array
     {
         $old           = $this->_states;
         $this->_states = $states;
@@ -746,11 +710,8 @@ public function setStates(array $states)
 
     /**
      * Set terminal states.
-     *
-     * @param   array   $terminal    Terminal states.
-     * @return  array
      */
-    public function setTerminal(array $terminal)
+    public function setTerminal(array $terminal): array
     {
         $old             = $this->_terminal;
         $this->_terminal = $terminal;
@@ -760,11 +721,8 @@ public function setTerminal(array $terminal)
 
     /**
      * Set transitions table.
-     *
-     * @param   array   $transitions    Transitions table.
-     * @return  array
      */
-    public function setTransitions(array $transitions)
+    public function setTransitions(array $transitions): array
     {
         $old                = $this->_transitions;
         $this->_transitions = $transitions;
@@ -774,11 +732,8 @@ public function setTransitions(array $transitions)
 
     /**
      * Set actions table.
-     *
-     * @param   array   $actions    Actions table.
-     * @return  array
      */
-    public function setActions(array $actions)
+    public function setActions(array $actions): array
     {
         foreach ($actions as $e => $automata) {
             foreach ($automata as $i => $state) {
@@ -798,11 +753,8 @@ public function setActions(array $actions)
 
     /**
      * Set names of automata.
-     *
-     * @param   array   $names    Names of automata.
-     * @return  array
      */
-    public function setNames(array $names)
+    public function setNames(array $names): array
     {
         $old          = $this->_names;
         $this->_names = $names;
@@ -812,90 +764,72 @@ public function setNames(array $names)
 
     /**
      * Get initial line.
-     *
-     * @return  int
      */
-    public function getInitialLine()
+    public function getInitialLine(): int
     {
         return $this->_initialLine;
     }
 
     /**
      * Get skip tokens.
-     *
-     * @return  array
      */
-    public function getSkip()
+    public function getSkip(): array
     {
         return $this->_skip;
     }
 
     /**
      * Get tokens.
-     *
-     * @return  array
      */
-    public function getTokens()
+    public function getTokens(): array
     {
         return $this->_tokens;
     }
 
     /**
      * Get states.
-     *
-     * @return  array
      */
-    public function getStates()
+    public function getStates(): array
     {
         return $this->_states;
     }
 
     /**
      * Get terminal states.
-     *
-     * @return  array
      */
-    public function getTerminal()
+    public function getTerminal(): array
     {
         return $this->_terminal;
     }
 
     /**
      * Get transitions table.
-     *
-     * @return  array
      */
-    public function getTransitions()
+    public function getTransitions(): array
     {
         return $this->_transitions;
     }
 
     /**
      * Get actions table.
-     *
-     * @return  array
      */
-    public function getActions()
+    public function getActions(): array
     {
         return $this->_actions;
     }
 
     /**
      * Get names of automata.
-     *
-     * @return  array
      */
-    public function getNames()
+    public function getNames(): array
     {
         return $this->_names;
     }
 
     /**
      * Enable cache
-     *
-     * @return  bool
      */
-    public static function enableCache()
+    public static function enableCache(): bool
     {
         $old                 = self::$_cacheEnabled;
         self::$_cacheEnabled = true;
@@ -905,10 +839,8 @@ public static function enableCache()
 
     /**
      * Disable cache
-     *
-     * @return  bool
      */
-    public static function disableCache()
+    public static function disableCache(): bool
     {
         $old                 = self::$_cacheEnabled;
         self::$_cacheEnabled = false;
@@ -918,8 +850,6 @@ public static function disableCache()
 
     /**
      * Transform automatas into DOT language.
-     *
-     * @return  void
      */
     public function __toString()
     {
diff --git a/Llk/Lexer.php b/Source/Llk/Lexer.php
similarity index 90%
rename from Llk/Lexer.php
rename to Source/Llk/Lexer.php
index 68513678..4cb2ea87 100644
--- a/Llk/Lexer.php
+++ b/Source/Llk/Lexer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,23 +44,20 @@
  * Class \Hoa\Compiler\Llk\Lexer.
  *
  * Lexical analyser, i.e. split a string into a set of lexeme, i.e. tokens.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Lexer
 {
     /**
      * Lexer state.
      *
-     * @var array
+     * @var ?string
      */
     protected $_lexerState  = null;
 
     /**
      * Text.
      *
-     * @var string
+     * @var ?string
      */
     protected $_text        = null;
 
@@ -79,7 +78,7 @@ class Lexer
     /**
      * PCRE options.
      *
-     * @var string
+     * @var ?string
      */
     protected $_pcreOptions = null;
 
@@ -87,8 +86,6 @@ class Lexer
 
     /**
      * Constructor.
-     *
-     * @param   array  $pragmas    Pragmas.
      */
     public function __construct(array $pragmas = [])
     {
@@ -102,13 +99,8 @@ public function __construct(array $pragmas = [])
     /**
      * Text tokenizer: splits the text in parameter in an ordered array of
      * tokens.
-     *
-     * @param   string  $text      Text to tokenize.
-     * @param   array   $tokens    Tokens to be returned.
-     * @return  \Generator
-     * @throws  \Hoa\Compiler\Exception\UnrecognizedToken
      */
-    public function lexMe($text, array $tokens)
+    public function lexMe(string $text, array $tokens): \Generator
     {
         $this->_text       = $text;
         $this->_tokens     = $tokens;
@@ -182,12 +174,8 @@ public function lexMe($text, array $tokens)
 
     /**
      * Compute the next token recognized at the beginning of the string.
-     *
-     * @param   int  $offset    Offset.
-     * @return  array
-     * @throws  \Hoa\Compiler\Exception\Lexer
      */
-    protected function nextToken($offset)
+    protected function nextToken(int $offset): ?array
     {
         $tokenArray = &$this->_tokens[$this->_lexerState];
 
@@ -263,14 +251,8 @@ protected function nextToken($offset)
 
     /**
      * Check if a given lexeme is matched at the beginning of the text.
-     *
-     * @param   string  $lexeme    Name of the lexeme.
-     * @param   string  $regex     Regular expression describing the lexeme.
-     * @param   int     $offset    Offset.
-     * @return  array
-     * @throws  \Hoa\Compiler\Exception\Lexer
      */
-    protected function matchLexeme($lexeme, $regex, $offset)
+    protected function matchLexeme(string $lexeme, string $regex, int $offset): ?array
     {
         $_regex = str_replace('#', '\#', $regex);
         $preg   = preg_match(
diff --git a/Llk/Llk.php b/Source/Llk/Llk.php
similarity index 91%
rename from Llk/Llk.php
rename to Source/Llk/Llk.php
index c4eb9482..9ca78dd1 100644
--- a/Llk/Llk.php
+++ b/Source/Llk/Llk.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -45,22 +47,16 @@
  *
  * This class provides a set of static helpers to manipulate (load and save) a
  * compiler more easily.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 abstract class Llk
 {
     /**
      * Load in-memory parser from a grammar description file.
      * The grammar description language is PP. See
-     * `hoa://Library/Compiler/Llk/Llk.pp` for an example, or the documentation.
-     *
-     * @param   \Hoa\Stream\IStream\In  $stream    Stream to read to grammar.
-     * @return  \Hoa\Compiler\Llk\Parser
-     * @throws  \Hoa\Compiler\Exception
+     * `hoa://Library/Compiler/Source/Llk/Llk.pp` for an example, or the
+     * documentation.
      */
-    public static function load(Stream\IStream\In $stream)
+    public static function load(Stream\IStream\In $stream): Parser
     {
         $pp = $stream->readAll();
 
@@ -96,12 +92,8 @@ public static function load(Stream\IStream\In $stream)
      * The generated PHP code will load the same in-memory parser. The state
      * will be reset. The parser will be saved as a class, named after
      * `$className`. To retrieve the parser, one must instanciate this class.
-     *
-     * @param   \Hoa\Compiler\Llk\Parser  $parser       Parser to save.
-     * @param   string                    $className    Parser classname.
-     * @return  string
      */
-    public static function save(Parser $parser, $className)
+    public static function save(Parser $parser, string $className): string
     {
         $out        = null;
         $outTokens  = null;
@@ -251,16 +243,8 @@ public static function save(Parser $parser, $className)
 
     /**
      * Parse the grammar description language.
-     *
-     * @param   string  $pp            Grammar description.
-     * @param   array   $tokens        Extracted tokens.
-     * @param   array   $rules         Extracted raw rules.
-     * @param   array   $pragmas       Extracted raw pragmas.
-     * @param   string  $streamName    The name of the stream containing the grammar.
-     * @return  void
-     * @throws  \Hoa\Compiler\Exception
      */
-    public static function parsePP($pp, &$tokens, &$rules, &$pragmas, $streamName)
+    public static function parsePP(string $pp, ?array &$tokens, ?array &$rules, ?array &$pragmas, string $streamName)
     {
         $lines   = explode("\n", $pp);
         $pragmas = [];
@@ -376,4 +360,4 @@ public static function parsePP($pp, &$tokens, &$rules, &$pragmas, $streamName)
 /**
  * Flex entity.
  */
-Consistency::flexEntity('Hoa\Compiler\Llk\Llk');
+Consistency::flexEntity(Llk::class);
diff --git a/Llk/Llk.pp b/Source/Llk/Llk.pp
similarity index 97%
rename from Llk/Llk.pp
rename to Source/Llk/Llk.pp
index 43cf29c5..d34f09fc 100644
--- a/Llk/Llk.pp
+++ b/Source/Llk/Llk.pp
@@ -35,9 +35,6 @@
 //
 // Provide grammar for the LL(k) parser.
 //
-// @copyright  Copyright © 2007-2017, Hoa community.
-// @license    New BSD License
-//
 
 
 %skip   space          \s
diff --git a/Llk/Parser.php b/Source/Llk/Parser.php
similarity index 87%
rename from Llk/Parser.php
rename to Source/Llk/Parser.php
index ec35d1d2..3cc4c9c9 100644
--- a/Llk/Parser.php
+++ b/Source/Llk/Parser.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -43,9 +45,6 @@
  * Class \Hoa\Compiler\Llk\Parser.
  *
  * LL(k) parser.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Parser
 {
@@ -54,14 +53,14 @@ class Parser
      *
      * @var array
      */
-    protected $_pragmas       = null;
+    protected $_pragmas       = [];
 
     /**
      * List of skipped tokens.
      *
      * @var array
      */
-    protected $_skip          = null;
+    protected $_skip          = [];
 
     /**
      * Associative array (token name => token regex), to be defined in
@@ -69,19 +68,19 @@ class Parser
      *
      * @var array
      */
-    protected $_tokens        = null;
+    protected $_tokens        = [];
 
     /**
      * Rules, to be defined as associative array, name => Rule object.
      *
      * @var array
      */
-    protected $_rules         = null;
+    protected $_rules         = [];
 
     /**
      * Lexer iterator.
      *
-     * @var \Hoa\Iterator\Lookahead
+     * @var Iterator\Lookahead
      */
     protected $_tokenSequence = null;
 
@@ -90,7 +89,7 @@ class Parser
      *
      * @var array
      */
-    protected $_errorToken    = null;
+    protected $_errorToken    = [];
 
     /**
      * Trace of activated rules.
@@ -104,12 +103,12 @@ class Parser
      *
      * @var array
      */
-    protected $_todo          = null;
+    protected $_todo          = [];
 
     /**
      * AST.
      *
-     * @var \Hoa\Compiler\Llk\TreeNode
+     * @var TreeNode
      */
     protected $_tree          = null;
 
@@ -124,10 +123,6 @@ class Parser
 
     /**
      * Construct the parser.
-     *
-     * @param   array  $tokens     Tokens.
-     * @param   array  $rules      Rules.
-     * @param   array  $pragmas    Pragmas.
      */
     public function __construct(
         array $tokens  = [],
@@ -143,14 +138,8 @@ public function __construct(
 
     /**
      * Parse :-).
-     *
-     * @param   string  $text    Text to parse.
-     * @param   string  $rule    The axiom, i.e. root rule.
-     * @param   bool    $tree    Whether build tree or not.
-     * @return  mixed
-     * @throws  \Hoa\Compiler\Exception\UnexpectedToken
      */
-    public function parse($text, $rule = null, $tree = true)
+    public function parse(string $text, ?string $rule = null, bool $tree = true)
     {
         $k = 1024;
 
@@ -180,7 +169,7 @@ public function parse($text, $rule = null, $tree = true)
         do {
             $out = $this->unfold();
 
-            if (null  !== $out &&
+            if (false  !== $out &&
                 'EOF' === $this->_tokenSequence->current()['token']) {
                 break;
             }
@@ -247,10 +236,8 @@ public function parse($text, $rule = null, $tree = true)
 
     /**
      * Unfold trace.
-     *
-     * @return  mixed
      */
-    protected function unfold()
+    private function unfold(): bool
     {
         while (0 < count($this->_todo)) {
             $rule = array_pop($this->_todo);
@@ -269,7 +256,7 @@ protected function unfold()
                 $out      = $this->_parse($zeRule, $next);
 
                 if (false === $out && false === $this->backtrack()) {
-                    return null;
+                    return false;
                 }
             }
         }
@@ -279,12 +266,8 @@ protected function unfold()
 
     /**
      * Parse current rule.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule  $zeRule    Current rule.
-     * @param   int                     $next      Next rule index.
-     * @return  bool
      */
-    protected function _parse(Rule $zeRule, $next)
+    private function _parse(Rule $zeRule, int $next): bool
     {
         if ($zeRule instanceof Rule\Token) {
             $name = $this->_tokenSequence->current()['token'];
@@ -454,10 +437,8 @@ protected function _parse(Rule $zeRule, $next)
 
     /**
      * Backtrack the trace.
-     *
-     * @return  bool
      */
-    protected function backtrack()
+    private function backtrack(): bool
     {
         $found = false;
 
@@ -495,12 +476,8 @@ protected function backtrack()
     /**
      * Build AST from trace.
      * Walk through the trace iteratively and recursively.
-     *
-     * @param   int      $i            Current trace index.
-     * @param   array    &$children    Collected children.
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    protected function _buildTree($i = 0, &$children = [])
+    private function _buildTree(int $i = 0, &$children = [])
     {
         $max = count($this->_trace);
 
@@ -613,20 +590,13 @@ protected function _buildTree($i = 0, &$children = [])
 
     /**
      * Try to merge directly children into an existing node.
-     *
-     * @param   array   &$children    Current children being gathering.
-     * @param   array   &$handle      Children of the new node.
-     * @param   string  $cId          Node ID.
-     * @param   bool    $recursive    Whether we should merge recursively or
-     *                                not.
-     * @return  bool
      */
     protected function mergeTree(
         &$children,
         &$handle,
-        $cId,
-        $recursive = false
-    ) {
+        string $cId,
+        bool $recursive = false
+    ): bool {
         end($children);
         $last = current($children);
 
@@ -657,10 +627,6 @@ protected function mergeTree(
     /**
      * Merge recursively.
      * Please, see self::mergeTree() to know the context.
-     *
-     * @param   \Hoa\Compiler\Llk\TreeNode  $node       Node that receives.
-     * @param   \Hoa\Compiler\Llk\TreeNode  $newNode    Node to merge.
-     * @return  void
      */
     protected function mergeTreeRecursive(TreeNode $node, TreeNode $newNode)
     {
@@ -693,61 +659,48 @@ protected function mergeTreeRecursive(TreeNode $node, TreeNode $newNode)
 
     /**
      * Get AST.
-     *
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function getTree()
+    public function getTree(): ?TreeNode
     {
         return $this->_tree;
     }
 
     /**
      * Get trace.
-     *
-     * @return  array
      */
-    public function getTrace()
+    public function getTrace(): array
     {
         return $this->_trace;
     }
 
     /**
      * Get pragmas.
-     *
-     * @return  array
      */
-    public function getPragmas()
+    public function getPragmas(): array
     {
         return $this->_pragmas;
     }
 
     /**
      * Get tokens.
-     *
-     * @return  array
      */
-    public function getTokens()
+    public function getTokens(): array
     {
         return $this->_tokens;
     }
 
     /**
      * Get the lexer iterator.
-     *
-     * @return  \Hoa\Iterator\Buffer
      */
-    public function getTokenSequence()
+    public function getTokenSequence(): ?Iterator\Buffer
     {
         return $this->_tokenSequence;
     }
 
     /**
      * Get rule by name.
-     *
-     * @param   string  $name    Rule name.
-     * @return  \Hoa\Compiler\Llk\Rule
      */
-    public function getRule($name)
+    public function getRule($name): ?Rule
     {
         if (!isset($this->_rules[$name])) {
             return null;
@@ -758,21 +711,21 @@ public function getRule($name)
 
     /**
      * Get rules.
-     *
-     * @return  array
      */
-    public function getRules()
+    public function getRules(): array
     {
         return $this->_rules;
     }
 
     /**
      * Get root rule.
-     *
-     * @return  string
      */
-    public function getRootRule()
+    public function getRootRule(): ?string
     {
+        if (empty($this->_rules)) {
+            return null;
+        }
+
         foreach ($this->_rules as $rule => $_) {
             if (!is_int($rule)) {
                 break;
diff --git a/Llk/Rule/Analyzer.php b/Source/Llk/Rule/Analyzer.php
similarity index 93%
rename from Llk/Rule/Analyzer.php
rename to Source/Llk/Rule/Analyzer.php
index 5156cef3..9bb06b74 100644
--- a/Llk/Rule/Analyzer.php
+++ b/Source/Llk/Rule/Analyzer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -43,9 +45,6 @@
  * Class \Hoa\Compiler\Llk\Rule\Analyzer.
  *
  * Analyze rules and transform them into atomic rules operations.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Analyzer
 {
@@ -75,7 +74,7 @@ class Analyzer
     /**
      * Lexer iterator.
      *
-     * @var \Hoa\Iterator\Lookahead
+     * @var ?Iterator\Lookahead
      */
     protected $_lexer                   = null;
 
@@ -84,19 +83,19 @@ class Analyzer
      *
      * @var array
      */
-    protected $_tokens                  = null;
+    protected $_tokens                  = [];
 
     /**
      * Rules.
      *
      * @var array
      */
-    protected $_rules                   = null;
+    protected $_rules                   = [];
 
     /**
      * Rule name being analyzed.
      *
-     * @var string
+     * @var ?string
      */
     private $_ruleName                  = null;
 
@@ -105,7 +104,7 @@ class Analyzer
      *
      * @var array
      */
-    protected $_parsedRules             = null;
+    protected $_parsedRules             = [];
 
     /**
      * Counter to auto-name transitional rules.
@@ -118,8 +117,6 @@ class Analyzer
 
     /**
      * Constructor.
-     *
-     * @param   array  $tokens    Tokens.
      */
     public function __construct(array $tokens)
     {
@@ -130,10 +127,6 @@ public function __construct(array $tokens)
 
    /**
      * Build the analyzer of the rules (does not analyze the rules).
-     *
-     * @param   array  $rules    Rule to be analyzed.
-     * @return  void
-     * @throws  \Hoa\Compiler\Exception
      */
     public function analyzeRules(array $rules)
     {
@@ -185,8 +178,6 @@ public function analyzeRules(array $rules)
 
     /**
      * Implementation of “rule”.
-     *
-     * @return  mixed
      */
     protected function rule(&$pNodeId)
     {
@@ -195,8 +186,6 @@ protected function rule(&$pNodeId)
 
     /**
      * Implementation of “choice”.
-     *
-     * @return  mixed
      */
     protected function choice(&$pNodeId)
     {
@@ -249,8 +238,6 @@ protected function choice(&$pNodeId)
 
     /**
      * Implementation of “concatenation”.
-     *
-     * @return  mixed
      */
     protected function concatenation(&$pNodeId)
     {
@@ -288,9 +275,6 @@ protected function concatenation(&$pNodeId)
 
     /**
      * Implementation of “repetition”.
-     *
-     * @return  mixed
-     * @throws  \Hoa\Compiler\Exception
      */
     protected function repetition(&$pNodeId)
     {
@@ -389,10 +373,6 @@ protected function repetition(&$pNodeId)
 
     /**
      * Implementation of “simple”.
-     *
-     * @return  mixed
-     * @throws  \Hoa\Compiler\Exception
-     * @throws  \Hoa\Compiler\Exception\Rule
      */
     protected function simple(&$pNodeId)
     {
@@ -428,7 +408,7 @@ protected function simple(&$pNodeId)
             foreach ($this->_tokens as $namespace => $tokens) {
                 foreach ($tokens as $token => $value) {
                     if ($token === $tokenName ||
-                        substr($token, 0, strpos($token, ':')) === $tokenName) {
+                        substr($token, 0, (int) strpos($token, ':')) === $tokenName) {
                         $exists = true;
 
                         break 2;
@@ -470,8 +450,8 @@ protected function simple(&$pNodeId)
 
             foreach ($this->_tokens as $namespace => $tokens) {
                 foreach ($tokens as $token => $value) {
-                    if ($token === $tokenName
-                       || substr($token, 0, strpos($token, ':')) === $tokenName) {
+                    if ($token === $tokenName ||
+                        substr($token, 0, (int) strpos($token, ':')) === $tokenName) {
                         $exists = true;
 
                         break 2;
diff --git a/Llk/Rule/Choice.php b/Source/Llk/Rule/Choice.php
similarity index 95%
rename from Llk/Rule/Choice.php
rename to Source/Llk/Rule/Choice.php
index 99d4ff45..e5207125 100644
--- a/Llk/Rule/Choice.php
+++ b/Source/Llk/Rule/Choice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Llk\Rule\Choice.
  *
  * The choice rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Choice extends Rule
 {
diff --git a/Llk/Rule/Concatenation.php b/Source/Llk/Rule/Concatenation.php
similarity index 95%
rename from Llk/Rule/Concatenation.php
rename to Source/Llk/Rule/Concatenation.php
index ac221550..e0aa353d 100644
--- a/Llk/Rule/Concatenation.php
+++ b/Source/Llk/Rule/Concatenation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Llk\Rule\Concatenation.
  *
  * The concatenation rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Concatenation extends Rule
 {
diff --git a/Llk/Rule/Ekzit.php b/Source/Llk/Rule/Ekzit.php
similarity index 95%
rename from Llk/Rule/Ekzit.php
rename to Source/Llk/Rule/Ekzit.php
index db4088df..a1d8afd7 100644
--- a/Llk/Rule/Ekzit.php
+++ b/Source/Llk/Rule/Ekzit.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -39,9 +41,6 @@
  * Class \Hoa\Compiler\Llk\Rule\Ekzit.
  *
  * The ekzit (exit) rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Ekzit extends Invocation
 {
diff --git a/Llk/Rule/Entry.php b/Source/Llk/Rule/Entry.php
similarity index 95%
rename from Llk/Rule/Entry.php
rename to Source/Llk/Rule/Entry.php
index c2c979b5..833e442b 100644
--- a/Llk/Rule/Entry.php
+++ b/Source/Llk/Rule/Entry.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,9 +42,6 @@
  * Class \Hoa\Compiler\Llk\Rule\Entry.
  *
  * The entry rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Entry extends Invocation
 {
diff --git a/Llk/Rule/Invocation.php b/Source/Llk/Rule/Invocation.php
similarity index 81%
rename from Llk/Rule/Invocation.php
rename to Source/Llk/Rule/Invocation.php
index 24cf946c..646176ff 100644
--- a/Llk/Rule/Invocation.php
+++ b/Source/Llk/Rule/Invocation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -40,16 +42,13 @@
  * Class \Hoa\Compiler\Llk\Rule\Invocation.
  *
  * Parent of entry and ekzit rules.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 abstract class Invocation
 {
     /**
      * Rule.
      *
-     * @var string
+     * @var mixed
      */
     protected $_rule         = null;
 
@@ -65,7 +64,7 @@ abstract class Invocation
      *
      * @var array
      */
-    protected $_todo         = null;
+    protected $_todo         = [];
 
     /**
      * Depth in the trace.
@@ -86,21 +85,16 @@ abstract class Invocation
 
     /**
      * Constructor.
-     *
-     * @param   string  $rule     Rule name.
-     * @param   mixed   $data     Data.
-     * @param   array   $todo     Todo.
-     * @param   int     $depth    Depth.
      */
     public function __construct(
         $rule,
         $data,
-        array $todo = null,
-        $depth      = -1
+        ?array $todo = null,
+        int $depth  = -1
     ) {
         $this->_rule         = $rule;
         $this->_data         = $data;
-        $this->_todo         = $todo;
+        $this->_todo         = $todo ?? [];
         $this->_depth        = $depth;
         $this->_transitional = is_int($rule);
 
@@ -109,8 +103,6 @@ public function __construct(
 
     /**
      * Get rule name.
-     *
-     * @return  string
      */
     public function getRule()
     {
@@ -119,8 +111,6 @@ public function getRule()
 
     /**
      * Get data.
-     *
-     * @return  mixed
      */
     public function getData()
     {
@@ -129,21 +119,16 @@ public function getData()
 
     /**
      * Get todo sequence.
-     *
-     * @return  array
      */
-    public function getTodo()
+    public function getTodo(): array
     {
         return $this->_todo;
     }
 
     /**
      * Set depth in trace.
-     *
-     * @param   int  $depth    Depth.
-     * @return  int
      */
-    public function setDepth($depth)
+    public function setDepth(int $depth): int
     {
         $old          = $this->_depth;
         $this->_depth = $depth;
@@ -153,20 +138,16 @@ public function setDepth($depth)
 
     /**
      * Get depth in trace.
-     *
-     * @return  int
      */
-    public function getDepth()
+    public function getDepth(): int
     {
         return $this->_depth;
     }
 
     /**
      * Check whether the rule is transitional or not.
-     *
-     * @return  bool
      */
-    public function isTransitional()
+    public function isTransitional(): bool
     {
         return $this->_transitional;
     }
diff --git a/Llk/Rule/Repetition.php b/Source/Llk/Rule/Repetition.php
similarity index 82%
rename from Llk/Rule/Repetition.php
rename to Source/Llk/Rule/Repetition.php
index a653272f..c180006b 100644
--- a/Llk/Rule/Repetition.php
+++ b/Source/Llk/Rule/Repetition.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,9 +44,6 @@
  * Class \Hoa\Compiler\Llk\Rule\Repetition.
  *
  * The repetition rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Repetition extends Rule
 {
@@ -66,14 +65,8 @@ class Repetition extends Rule
 
     /**
      * Constructor.
-     *
-     * @param   string  $name        Name.
-     * @param   int     $min         Minimum bound.
-     * @param   int     $max         Maximum bound.
-     * @param   mixed   $children    Children.
-     * @param   string  $nodeId      Node ID.
      */
-    public function __construct($name, $min, $max, $children, $nodeId)
+    public function __construct($name, $min, $max, $children, ?string $nodeId)
     {
         parent::__construct($name, $children, $nodeId);
 
@@ -96,30 +89,24 @@ public function __construct($name, $min, $max, $children, $nodeId)
 
     /**
      * Get minimum bound.
-     *
-     * @return  int
      */
-    public function getMin()
+    public function getMin(): int
     {
         return $this->_min;
     }
 
     /**
      * Get maximum bound.
-     *
-     * @return  int
      */
-    public function getMax()
+    public function getMax(): int
     {
         return $this->_max;
     }
 
     /**
      * Check whether the maximum repetition is unbounded.
-     *
-     * @return   bool
      */
-    public function isInfinite()
+    public function isInfinite(): bool
     {
         return -1 === $this->getMax();
     }
diff --git a/Llk/Rule/Rule.php b/Source/Llk/Rule/Rule.php
similarity index 77%
rename from Llk/Rule/Rule.php
rename to Source/Llk/Rule/Rule.php
index 1a0b5666..e2719bf1 100644
--- a/Llk/Rule/Rule.php
+++ b/Source/Llk/Rule/Rule.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,16 +44,13 @@
  * Class \Hoa\Compiler\Llk\Rule.
  *
  * Rule parent.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 abstract class Rule
 {
     /**
      * Rule name.
      *
-     * @var string
+     * @var mixed
      */
     protected $_name           = null;
 
@@ -65,7 +64,7 @@ abstract class Rule
     /**
      * Node ID.
      *
-     * @var string
+     * @var ?string
      */
     protected $_nodeId         = null;
 
@@ -79,7 +78,7 @@ abstract class Rule
     /**
      * Default ID.
      *
-     * @var string
+     * @var ?string
      */
     protected $_defaultId      = null;
 
@@ -93,7 +92,7 @@ abstract class Rule
     /**
      * For non-transitional rule: PP representation.
      *
-     * @var string
+     * @var ?string
      */
     protected $_pp             = null;
 
@@ -109,12 +108,8 @@ abstract class Rule
 
     /**
      * Constructor.
-     *
-     * @param   string  $name        Rule name.
-     * @param   mixed   $children    Children.
-     * @param   string  $nodeId      Node ID.
      */
-    public function __construct($name, $children, $nodeId = null)
+    public function __construct($name, $children, ?string $nodeId = null)
     {
         $this->setName($name);
         $this->setChildren($children);
@@ -125,9 +120,6 @@ public function __construct($name, $children, $nodeId = null)
 
     /**
      * Set rule name.
-     *
-     * @param   string  $name    Rule name.
-     * @return  string
      */
     public function setName($name)
     {
@@ -139,8 +131,6 @@ public function setName($name)
 
     /**
      * Get rule name.
-     *
-     * @return  string
      */
     public function getName()
     {
@@ -149,9 +139,6 @@ public function getName()
 
     /**
      * Set rule's children.
-     *
-     * @param   mixed  $children    Children.
-     * @return  mixed
      */
     protected function setChildren($children)
     {
@@ -163,8 +150,6 @@ protected function setChildren($children)
 
     /**
      * Get rule's children.
-     *
-     * @return  mixed
      */
     public function getChildren()
     {
@@ -173,20 +158,17 @@ public function getChildren()
 
     /**
      * Set node ID.
-     *
-     * @param   string  $nodeId    Node ID.
-     * @return  string
      */
-    public function setNodeId($nodeId)
+    public function setNodeId(?string $nodeId): ?string
     {
         $old = $this->_nodeId;
 
-        if (false !== $pos = strpos($nodeId, ':')) {
-            $this->_nodeId      = substr($nodeId, 0, $pos);
-            $this->_nodeOptions = str_split(substr($nodeId, $pos + 1));
-        } else {
+        if (empty($nodeId) || false === $pos = strpos($nodeId, ':')) {
             $this->_nodeId      = $nodeId;
             $this->_nodeOptions = [];
+        } else {
+            $this->_nodeId      = substr($nodeId, 0, $pos);
+            $this->_nodeOptions = str_split(substr($nodeId, $pos + 1));
         }
 
         return $old;
@@ -194,31 +176,24 @@ public function setNodeId($nodeId)
 
     /**
      * Get node ID.
-     *
-     * @return  string
      */
-    public function getNodeId()
+    public function getNodeId(): ?string
     {
         return $this->_nodeId;
     }
 
     /**
      * Get node options.
-     *
-     * @retrun  array
      */
-    public function getNodeOptions()
+    public function getNodeOptions(): array
     {
         return $this->_nodeOptions;
     }
 
     /**
      * Set default ID.
-     *
-     * @param   string  $defaultId    Default ID.
-     * @return  string
      */
-    public function setDefaultId($defaultId)
+    public function setDefaultId(string $defaultId): ?string
     {
         $old = $this->_defaultId;
 
@@ -235,31 +210,24 @@ public function setDefaultId($defaultId)
 
     /**
      * Get default ID.
-     *
-     * @return  string
      */
-    public function getDefaultId()
+    public function getDefaultId(): ?string
     {
         return $this->_defaultId;
     }
 
     /**
      * Get default options.
-     *
-     * @return  array
      */
-    public function getDefaultOptions()
+    public function getDefaultOptions(): array
     {
         return $this->_defaultOptions;
     }
 
     /**
      * Set PP representation of the rule.
-     *
-     * @param   string  $pp    PP representation.
-     * @return  string
      */
-    public function setPPRepresentation($pp)
+    public function setPPRepresentation(string $pp): ?string
     {
         $old                 = $this->_pp;
         $this->_pp           = $pp;
@@ -270,20 +238,16 @@ public function setPPRepresentation($pp)
 
     /**
      * Get PP representation of the rule.
-     *
-     * @return  string
      */
-    public function getPPRepresentation()
+    public function getPPRepresentation(): ?string
     {
         return $this->_pp;
     }
 
     /**
      * Check whether the rule is transitional or not.
-     *
-     * @return  bool
      */
-    public function isTransitional()
+    public function isTransitional(): bool
     {
         return $this->_transitional;
     }
@@ -292,4 +256,4 @@ public function isTransitional()
 /**
  * Flex entity.
  */
-Consistency::flexEntity('Hoa\Compiler\Llk\Rule\Rule');
+Consistency::flexEntity(Rule::class);
diff --git a/Llk/Rule/Token.php b/Source/Llk/Rule/Token.php
similarity index 74%
rename from Llk/Rule/Token.php
rename to Source/Llk/Rule/Token.php
index bd49564a..7081cb0a 100644
--- a/Llk/Rule/Token.php
+++ b/Source/Llk/Rule/Token.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -43,16 +45,13 @@
  * Class \Hoa\Compiler\Llk\Rule\Token.
  *
  * The token rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Token extends Rule
 {
     /**
      * LL(k) compiler of hoa://Library/Regex/Grammar.pp.
      *
-     * @var \Hoa\Compiler\Llk\Parser
+     * @var ?Compiler\Llk\Parser
      */
     protected static $_regexCompiler = null;
 
@@ -66,7 +65,7 @@ class Token extends Rule
     /**
      * Namespace.
      *
-     * @var string
+     * @var ?string
      */
     protected $_namespace            = null;
 
@@ -80,14 +79,14 @@ class Token extends Rule
     /**
      * AST of the regex.
      *
-     * @var \Hoa\Compiler\Llk\TreeNode
+     * @var ?Compiler\Llk\TreeNode
      */
     protected $_ast                  = null;
 
     /**
      * Token value.
      *
-     * @var string
+     * @var ?string
      */
     protected $_value                = null;
 
@@ -114,19 +113,13 @@ class Token extends Rule
 
     /**
      * Constructor.
-     *
-     * @param   string  $name           Name.
-     * @param   string  $tokenName      Token name.
-     * @param   string  $nodeId         Node ID.
-     * @param   int     $unification    Unification index.
-     * @param   bool    $kept           Whether the token is kept or not in the AST.
      */
     public function __construct(
         $name,
-        $tokenName,
-        $nodeId,
-        $unification,
-        $kept = false
+        string $tokenName,
+        ?string $nodeId,
+        int $unification,
+        bool $kept = false
     ) {
         parent::__construct($name, null, $nodeId);
 
@@ -139,21 +132,16 @@ public function __construct(
 
     /**
      * Get token name.
-     *
-     * @return  string
      */
-    public function getTokenName()
+    public function getTokenName(): string
     {
         return $this->_tokenName;
     }
 
     /**
      * Set token namespace.
-     *
-     * @param   string  $namespace    Namespace.
-     * @return  string
      */
-    public function setNamespace($namespace)
+    public function setNamespace(string $namespace): ?string
     {
         $old              = $this->_namespace;
         $this->_namespace = $namespace;
@@ -163,21 +151,16 @@ public function setNamespace($namespace)
 
     /**
      * Get token namespace.
-     *
-     * @return  string
      */
-    public function getNamespace()
+    public function getNamespace(): ?string
     {
         return $this->_namespace;
     }
 
     /**
      * Set representation.
-     *
-     * @param   string  $regex    Representation.
-     * @return  string
      */
-    public function setRepresentation($regex)
+    public function setRepresentation(string $regex): ?string
     {
         $old          = $this->_regex;
         $this->_regex = $regex;
@@ -187,20 +170,16 @@ public function setRepresentation($regex)
 
     /**
      * Get token representation.
-     *
-     * @return  string
      */
-    public function getRepresentation()
+    public function getRepresentation(): ?string
     {
         return $this->_regex;
     }
 
     /**
      * Get AST of the token representation.
-     *
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function getAST()
+    public function getAST(): Compiler\Llk\TreeNode
     {
         if (null === static::$_regexCompiler) {
             $stream = new File\Read('hoa://Library/Regex/Grammar.pp');
@@ -220,11 +199,8 @@ public function getAST()
 
     /**
      * Set token value.
-     *
-     * @param   string  $value    Value.
-     * @return  string
      */
-    public function setValue($value)
+    public function setValue(string $value): ?string
     {
         $old          = $this->_value;
         $this->_value = $value;
@@ -234,21 +210,16 @@ public function setValue($value)
 
     /**
      * Get token value.
-     *
-     * @return  string
      */
-    public function getValue()
+    public function getValue(): ?string
     {
         return $this->_value;
     }
 
     /**
      * Set token offset.
-     *
-     * @param   int  $offset    Offset.
-     * @return  int
      */
-    public function setOffset($offset)
+    public function setOffset(int $offset): int
     {
         $old           = $this->_offset;
         $this->_offset = $offset;
@@ -258,21 +229,16 @@ public function setOffset($offset)
 
     /**
      * Get token offset.
-     *
-     * @return int
      */
-    public function getOffset()
+    public function getOffset(): int
     {
         return $this->_offset;
     }
 
     /**
      * Set whether the token is kept or not in the AST.
-     *
-     * @param   bool  $kept    Kept.
-     * @return  bool
      */
-    public function setKept($kept)
+    public function setKept(bool $kept): bool
     {
         $old         = $this->_kept;
         $this->_kept = $kept;
@@ -282,20 +248,16 @@ public function setKept($kept)
 
     /**
      * Check whether the token is kept in the AST or not.
-     *
-     * @return  bool
      */
-    public function isKept()
+    public function isKept(): bool
     {
         return $this->_kept;
     }
 
     /**
      * Get unification index.
-     *
-     * @return  int
      */
-    public function getUnificationIndex()
+    public function getUnificationIndex(): int
     {
         return $this->_unification;
     }
diff --git a/Llk/Sampler/BoundedExhaustive.php b/Source/Llk/Sampler/BoundedExhaustive.php
similarity index 88%
rename from Llk/Sampler/BoundedExhaustive.php
rename to Source/Llk/Sampler/BoundedExhaustive.php
index 3dca3c43..1c630086 100644
--- a/Llk/Sampler/BoundedExhaustive.php
+++ b/Source/Llk/Sampler/BoundedExhaustive.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -47,9 +49,6 @@
  * size n (bounded).
  * This algorithm is based on multiset (set with repetition).
  * Repetition unfolding: upper bound of + and * is set to n.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class BoundedExhaustive extends Sampler implements Iterator
 {
@@ -58,14 +57,14 @@ class BoundedExhaustive extends Sampler implements Iterator
      *
      * @var array
      */
-    protected $_todo    = null;
+    protected $_todo    = [];
 
     /**
      * Stack of rules that have already been covered.
      *
      * @var array
      */
-    protected $_trace   = null;
+    protected $_trace   = [];
 
     /**
      * Current iterator key.
@@ -77,7 +76,7 @@ class BoundedExhaustive extends Sampler implements Iterator
     /**
      * Current iterator value.
      *
-     * @var string
+     * @var ?string
      */
     protected $_current = null;
 
@@ -92,46 +91,36 @@ class BoundedExhaustive extends Sampler implements Iterator
 
     /**
      * Construct a generator.
-     *
-     * @param   \Hoa\Compiler\Llk\Parser  $compiler        Compiler/parser.
-     * @param   \Hoa\Visitor\Visit        $tokenSampler    Token sampler.
-     * @param   int                       $length          Max data length.
      */
     public function __construct(
         Compiler\Llk\Parser $compiler,
         Visitor\Visit       $tokenSampler,
-        $length = 5
+        int $maximumLength = 5
     ) {
         parent::__construct($compiler, $tokenSampler);
-        $this->setLength($length);
+        $this->setLength($maximumLength);
 
         return;
     }
 
     /**
      * Get the current iterator value.
-     *
-     * @return  string
      */
-    public function current()
+    public function current(): ?string
     {
         return $this->_current;
     }
 
     /**
      * Get the current iterator key.
-     *
-     * @return  int
      */
-    public function key()
+    public function key(): int
     {
         return $this->_key;
     }
 
     /**
      * Useless here.
-     *
-     * @return  void
      */
     public function next()
     {
@@ -140,8 +129,6 @@ public function next()
 
     /**
      * Rewind the internal iterator pointer.
-     *
-     * @return  void
      */
     public function rewind()
     {
@@ -160,10 +147,8 @@ public function rewind()
 
     /**
      * Compute the current iterator value, i.e. generate a new solution.
-     *
-     * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         if (false === $this->unfold()) {
             return false;
@@ -185,10 +170,8 @@ public function valid()
 
     /**
      * Unfold rules from the todo stack.
-     *
-     * @return  bool
      */
-    protected function unfold()
+    protected function unfold(): bool
     {
         while (0 < count($this->_todo)) {
             $pop = array_pop($this->_todo);
@@ -212,12 +195,8 @@ protected function unfold()
 
     /**
      * The bounded-exhaustive algorithm.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule  $rule    Rule to cover.
-     * @param   int                     $next    Next rule.
-     * @return  bool
      */
-    protected function boundedExhaustive(Compiler\Llk\Rule $rule, $next)
+    protected function boundedExhaustive(Compiler\Llk\Rule $rule, int $next): bool
     {
         $children = $rule->getChildren();
 
@@ -322,10 +301,8 @@ protected function boundedExhaustive(Compiler\Llk\Rule $rule, $next)
 
     /**
      * Backtrack to the previous choice-point.
-     *
-     * @return  bool
      */
-    protected function backtrack()
+    protected function backtrack(): bool
     {
         $found = false;
 
@@ -359,12 +336,8 @@ protected function backtrack()
 
     /**
      * Set upper-bound, the maximum data length.
-     *
-     * @param   int  $length    Length.
-     * @return  int
-     * @throws  \Hoa\Compiler\Exception
      */
-    public function setLength($length)
+    public function setLength(int $length): int
     {
         if (0 >= $length) {
             throw new Exception(
@@ -382,10 +355,8 @@ public function setLength($length)
 
     /**
      * Get upper-bound.
-     *
-     * @return  int
      */
-    public function getLength()
+    public function getLength(): int
     {
         return $this->_length;
     }
diff --git a/Llk/Sampler/Coverage.php b/Source/Llk/Sampler/Coverage.php
similarity index 93%
rename from Llk/Sampler/Coverage.php
rename to Source/Llk/Sampler/Coverage.php
index 1755ca3b..c7b8ed77 100644
--- a/Llk/Sampler/Coverage.php
+++ b/Source/Llk/Sampler/Coverage.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -55,9 +57,6 @@
  *      • * is bounded to 0, 1 or 2;
  *      • + is unfolded 1 or 2 times;
  *      • {x,y} is unfolded x, x + 1, y - 1 and y times.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Coverage extends Sampler implements Iterator
 {
@@ -66,21 +65,21 @@ class Coverage extends Sampler implements Iterator
      *
      * @var array
      */
-    protected $_todo         = null;
+    protected $_todo         = [];
 
     /**
      * Stack of rules that have already been covered.
      *
      * @var array
      */
-    protected $_trace        = null;
+    protected $_trace        = [];
 
     /**
      * Produced test cases.
      *
      * @var array
      */
-    protected $_tests        = null;
+    protected $_tests        = [];
 
     /**
      * Covered rules: ruleName to structure that contains the choice point and
@@ -88,7 +87,7 @@ class Coverage extends Sampler implements Iterator
      *
      * @var array
      */
-    protected $_coveredRules = null;
+    protected $_coveredRules = [];
 
     /**
      * Current iterator key.
@@ -100,7 +99,7 @@ class Coverage extends Sampler implements Iterator
     /**
      * Current iterator value.
      *
-     * @var string
+     * @var ?string
      */
     protected $_current      = null;
 
@@ -108,28 +107,22 @@ class Coverage extends Sampler implements Iterator
 
     /**
      * Get the current iterator value.
-     *
-     * @return  string
      */
-    public function current()
+    public function current(): ?string
     {
         return $this->_current;
     }
 
     /**
      * Get the current iterator key.
-     *
-     * @return  int
      */
-    public function key()
+    public function key(): int
     {
         return $this->_key;
     }
 
     /**
      * Useless here.
-     *
-     * @return  void
      */
     public function next()
     {
@@ -138,8 +131,6 @@ public function next()
 
     /**
      * Rewind the internal iterator pointer.
-     *
-     * @return  void
      */
     public function rewind()
     {
@@ -179,10 +170,8 @@ public function rewind()
 
     /**
      * Compute the current iterator value, i.e. generate a new solution.
-     *
-     * @return  bool
      */
-    public function valid()
+    public function valid(): bool
     {
         $ruleName = $this->_rootRuleName;
 
@@ -228,10 +217,8 @@ public function valid()
 
     /**
      * Unfold rules from the todo stack.
-     *
-     * @return  bool
      */
-    protected function unfold()
+    protected function unfold(): bool
     {
         while (0 < count($this->_todo)) {
             $pop = array_pop($this->_todo);
@@ -253,11 +240,8 @@ protected function unfold()
 
     /**
      * The coverage algorithm.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule  $rule    Rule to cover.
-     * @return  bool
      */
-    protected function coverage(Compiler\Llk\Rule $rule)
+    protected function coverage(Compiler\Llk\Rule $rule): bool
     {
         $children = $rule->getChildren();
 
@@ -457,11 +441,8 @@ protected function coverage(Compiler\Llk\Rule $rule)
 
     /**
      * Extract a given sequence from existing traces.
-     *
-     * @param   array  $rules    Rules to consider.
-     * @return  array
      */
-    protected function extract(array $rules)
+    protected function extract(array $rules): ?array
     {
         $out = [];
 
@@ -521,10 +502,8 @@ protected function extract(array $rules)
 
     /**
      * Backtrack to the previous choice-point.
-     *
-     * @return  bool
      */
-    protected function backtrack()
+    protected function backtrack(): bool
     {
         $found = false;
 
@@ -556,9 +535,6 @@ protected function backtrack()
 
     /**
      * Update coverage of a rule.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule\Ekzit  $rule    Rule to consider.
-     * @return  void
      */
     protected function updateCoverage(Compiler\Llk\Rule\Ekzit $Rule)
     {
@@ -611,11 +587,8 @@ protected function updateCoverage(Compiler\Llk\Rule\Ekzit $Rule)
 
     /**
      * Check if all rules have been entirely covered.
-     *
-     * @param   string  $ruleName    Rule name.
-     * @return  bool
      */
-    protected function allCovered($ruleName)
+    protected function allCovered($ruleName): bool
     {
         foreach ($this->_coveredRules[$ruleName] as $value) {
             if (1 !== $value) {
@@ -628,11 +601,8 @@ protected function allCovered($ruleName)
 
     /**
      * Check if a rule is a root rule that is currently being processed.
-     *
-     * @param   string  $ruleName    Rule name.
-     * @return  bool
      */
-    protected function checkRuleRoot($ruleName)
+    protected function checkRuleRoot($ruleName): bool
     {
         if (true === $this->_rules[$ruleName]->isTransitional()) {
             return false;
diff --git a/Llk/Sampler/Exception.php b/Source/Llk/Sampler/Exception.php
similarity index 95%
rename from Llk/Sampler/Exception.php
rename to Source/Llk/Sampler/Exception.php
index 453ab777..bba9631f 100644
--- a/Llk/Sampler/Exception.php
+++ b/Source/Llk/Sampler/Exception.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,9 +44,6 @@
  * Class \Hoa\Compiler\Llk\Sampler\Exception.
  *
  * Extending the \Hoa\Compiler\Exception class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Exception extends Compiler\Exception
 {
diff --git a/Llk/Sampler/Sampler.php b/Source/Llk/Sampler/Sampler.php
similarity index 84%
rename from Llk/Sampler/Sampler.php
rename to Source/Llk/Sampler/Sampler.php
index d793e8e2..9f5dd8b1 100644
--- a/Llk/Sampler/Sampler.php
+++ b/Source/Llk/Sampler/Sampler.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,16 +46,13 @@
  * Class \Hoa\Compiler\Llk\Sampler.
  *
  * Sampler parent.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 abstract class Sampler
 {
     /**
      * Compiler.
      *
-     * @var \Hoa\Compiler\Llk\Parser
+     * @var Compiler\Llk\Parser
      */
     protected $_compiler         = null;
 
@@ -62,26 +61,26 @@ abstract class Sampler
      *
      * @var array
      */
-    protected $_tokens           = null;
+    protected $_tokens           = [];
 
     /**
      * All rules (from the compiler).
      *
      * @var array
      */
-    protected $_rules            = null;
+    protected $_rules            = [];
 
     /**
      * Token sampler.
      *
-     * @var \Hoa\Visitor\Visit
+     * @var Visitor\Visit
      */
     protected $_tokenSampler     = null;
 
     /**
      * Root rule name.
      *
-     * @var string
+     * @var ?string
      */
     protected $_rootRuleName     = null;
 
@@ -102,9 +101,6 @@ abstract class Sampler
 
     /**
      * Construct a generator.
-     *
-     * @param   \Hoa\Compiler\Llk\Parser  $compiler        Compiler/parser.
-     * @param   \Hoa\Visitor\Visit        $tokenSampler    Token sampler.
      */
     public function __construct(
         Compiler\Llk\Parser $compiler,
@@ -121,20 +117,16 @@ public function __construct(
 
     /**
      * Get compiler.
-     *
-     * @return  \Hoa\Compiler\Llk\Parser
      */
-    public function getCompiler()
+    public function getCompiler(): Compiler\Llk\Parser
     {
         return $this->_compiler;
     }
 
     /**
      * Get the AST of the current namespace skip token.
-     *
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    protected function getSkipTokenAST()
+    protected function getSkipTokenAST(): Compiler\Llk\TreeNode
     {
         if (!isset($this->_skipTokenAST[$this->_currentNamespace])) {
             $token = new Compiler\Llk\Rule\Token(
@@ -157,11 +149,8 @@ protected function getSkipTokenAST()
     /**
      * Complete a token (namespace and representation).
      * It returns the next namespace.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule\Token  $token    Token.
-     * @return  string
      */
-    protected function completeToken(Compiler\Llk\Rule\Token $token)
+    protected function completeToken(Compiler\Llk\Rule\Token $token): string
     {
         if (null !== $token->getRepresentation()) {
             return $this->_currentNamespace;
@@ -196,11 +185,8 @@ protected function completeToken(Compiler\Llk\Rule\Token $token)
 
     /**
      * Set current token namespace.
-     *
-     * @param   string  $namespace    Token namespace.
-     * @return  string
      */
-    protected function setCurrentNamespace($namespace)
+    protected function setCurrentNamespace(string $namespace): string
     {
         $old                     = $this->_currentNamespace;
         $this->_currentNamespace = $namespace;
@@ -211,11 +197,8 @@ protected function setCurrentNamespace($namespace)
     /**
      * Generate a token value.
      * Complete and set next token namespace.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule\Token  $token    Token.
-     * @return  string
      */
-    protected function generateToken(Compiler\Llk\Rule\Token $token)
+    protected function generateToken(Compiler\Llk\Rule\Token $token): string
     {
         $toNamespace = $this->completeToken($token);
         $this->setCurrentNamespace($toNamespace);
@@ -233,4 +216,4 @@ protected function generateToken(Compiler\Llk\Rule\Token $token)
 /**
  * Flex entity.
  */
-Consistency::flexEntity('Hoa\Compiler\Llk\Sampler\Sampler');
+Consistency::flexEntity(Sampler::class);
diff --git a/Llk/Sampler/Uniform.php b/Source/Llk/Sampler/Uniform.php
similarity index 90%
rename from Llk/Sampler/Uniform.php
rename to Source/Llk/Sampler/Uniform.php
index f15ac9dc..151080c8 100644
--- a/Llk/Sampler/Uniform.php
+++ b/Source/Llk/Sampler/Uniform.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -48,9 +50,6 @@
  * size n. The counting helps to compute cumulative distribution functions,
  * which guide the exploration.
  * Repetition unfolding: upper bound of + and * is set to n.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Uniform extends Sampler
 {
@@ -72,9 +71,6 @@ class Uniform extends Sampler
 
     /**
      * Construct a generator.
-     *
-     * @param   \Hoa\Compiler\Llk\Parser  $compiler        Compiler/parser.
-     * @param   \Hoa\Visitor\Visit        $tokenSampler    Token sampler.
      */
     public function __construct(
         Compiler\Llk\Parser $compiler,
@@ -95,12 +91,8 @@ public function __construct(
 
     /**
      * The random and uniform algorithm.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule  $rule    Rule to start.
-     * @param   int                     $n       Size.
-     * @return  string
      */
-    public function uniform(Compiler\Llk\Rule $rule = null, $n = -1)
+    public function uniform(Compiler\Llk\Rule $rule = null, int $n = -1): ?string
     {
         if (null === $rule && -1 === $n) {
             $rule = $this->_rules[$this->_rootRuleName];
@@ -170,12 +162,8 @@ public function uniform(Compiler\Llk\Rule $rule = null, $n = -1)
 
     /**
      * Recursive method applied to our problematic.
-     *
-     * @param   \Hoa\Compiler\Llk\Rule  $rule    Rule to start.
-     * @param   int                     $n       Size.
-     * @return  int
      */
-    public function count(Compiler\Llk\Rule $rule = null, $n = -1)
+    public function count(Compiler\Llk\Rule $rule = null, int $n = -1): int
     {
         if (null === $rule || -1 === $n) {
             return 0;
@@ -265,12 +253,8 @@ public function count(Compiler\Llk\Rule $rule = null, $n = -1)
 
     /**
      * Set upper-bound, the maximum data length.
-     *
-     * @param   int  $length    Length.
-     * @return  int
-     * @throws  \Hoa\Compiler\Exception
      */
-    public function setLength($length)
+    public function setLength(int $length): int
     {
         if (0 >= $length) {
             throw new Exception(
@@ -292,10 +276,8 @@ public function setLength($length)
 
     /**
      * Get upper-bound.
-     *
-     * @return  int
      */
-    public function getLength()
+    public function getLength(): int
     {
         return $this->_length;
     }
diff --git a/Llk/TreeNode.php b/Source/Llk/TreeNode.php
similarity index 73%
rename from Llk/TreeNode.php
rename to Source/Llk/TreeNode.php
index 1ea4e781..23bb1934 100644
--- a/Llk/TreeNode.php
+++ b/Source/Llk/TreeNode.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,9 +44,6 @@
  * Class \Hoa\Compiler\Llk\TreeNode.
  *
  * Provide a generic node for the AST produced by LL(k) parser.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class TreeNode implements Visitor\Element
 {
@@ -67,7 +66,7 @@ class TreeNode implements Visitor\Element
      *
      * @var array
      */
-    protected $_children = null;
+    protected $_children = [];
 
     /**
      * Parent.
@@ -94,7 +93,7 @@ class TreeNode implements Visitor\Element
      * @param   \Hoa\Compiler\Llk\TreeNode  $parent    Parent.
      */
     public function __construct(
-        $id,
+        string $id,
         array $value    = null,
         array $children = [],
         self  $parent   = null
@@ -116,11 +115,8 @@ public function __construct(
 
     /**
      * Set ID.
-     *
-     * @param   string  $id    ID.
-     * @return  string
      */
-    public function setId($id)
+    public function setId(string $id): ?string
     {
         $old       = $this->_id;
         $this->_id = $id;
@@ -130,21 +126,16 @@ public function setId($id)
 
     /**
      * Get ID.
-     *
-     * @return  string
      */
-    public function getId()
+    public function getId(): string
     {
         return $this->_id;
     }
 
     /**
      * Set value.
-     *
-     * @param   array  $value    Value (token & value).
-     * @return  array
      */
-    public function setValue(array $value)
+    public function setValue(array $value): ?array
     {
         $old          = $this->_value;
         $this->_value = $value;
@@ -154,20 +145,16 @@ public function setValue(array $value)
 
     /**
      * Get value.
-     *
-     * @return  array
      */
-    public function getValue()
+    public function getValue(): ?array
     {
         return $this->_value;
     }
 
     /**
      * Get value token.
-     *
-     * @return  string
      */
-    public function getValueToken()
+    public function getValueToken(): ?string
     {
         return
             isset($this->_value['token'])
@@ -177,10 +164,8 @@ public function getValueToken()
 
     /**
      * Get value value.
-     *
-     * @return  string
      */
-    public function getValueValue()
+    public function getValueValue(): ?string
     {
         return
             isset($this->_value['value'])
@@ -190,10 +175,8 @@ public function getValueValue()
 
     /**
      * Get token offset.
-     *
-     * @return  int
      */
-    public function getOffset()
+    public function getOffset(): int
     {
         return
             isset($this->_value['offset'])
@@ -203,21 +186,16 @@ public function getOffset()
 
     /**
      * Check if the node represents a token or not.
-     *
-     * @return  bool
      */
-    public function isToken()
+    public function isToken(): bool
     {
         return !empty($this->_value);
     }
 
     /**
      * Prepend a child.
-     *
-     * @param   \Hoa\Compiler\Llk\TreeNode  $child    Child.
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function prependChild(TreeNode $child)
+    public function prependChild(self $child): self
     {
         array_unshift($this->_children, $child);
 
@@ -226,11 +204,8 @@ public function prependChild(TreeNode $child)
 
     /**
      * Append a child.
-     *
-     * @param   \Hoa\Compiler\Llk\TreeNode  $child    Child.
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function appendChild(TreeNode $child)
+    public function appendChild(self $child): self
     {
         $this->_children[] = $child;
 
@@ -239,11 +214,8 @@ public function appendChild(TreeNode $child)
 
     /**
      * Set children.
-     *
-     * @param   array  $children    Children.
-     * @return  array
      */
-    public function setChildren(array $children)
+    public function setChildren(array $children): array
     {
         $old             = $this->_children;
         $this->_children = $children;
@@ -253,11 +225,8 @@ public function setChildren(array $children)
 
     /**
      * Get child.
-     *
-     * @param   int  $i    Index.
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function getChild($i)
+    public function getChild(int $i): ?TreeNode
     {
         return
             true === $this->childExists($i)
@@ -267,42 +236,32 @@ public function getChild($i)
 
     /**
      * Get children.
-     *
-     * @return  array
      */
-    public function getChildren()
+    public function getChildren(): array
     {
         return $this->_children;
     }
 
     /**
      * Get number of children.
-     *
-     * @return  int
      */
-    public function getChildrenNumber()
+    public function getChildrenNumber(): int
     {
         return count($this->_children);
     }
 
     /**
      * Check if a child exists.
-     *
-     * @param   int  $i    Index.
-     * @return  bool
      */
-    public function childExists($i)
+    public function childExists(int $i): bool
     {
         return array_key_exists($i, $this->_children);
     }
 
     /**
      * Set parent.
-     *
-     * @param   \Hoa\Compiler\Llk\TreeNode  $parent    Parent.
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function setParent(TreeNode $parent)
+    public function setParent(self $parent): ?self
     {
         $old           = $this->_parent;
         $this->_parent = $parent;
@@ -312,31 +271,22 @@ public function setParent(TreeNode $parent)
 
     /**
      * Get parent.
-     *
-     * @return  \Hoa\Compiler\Llk\TreeNode
      */
-    public function getParent()
+    public function getParent(): ?self
     {
         return $this->_parent;
     }
 
     /**
      * Get data.
-     *
-     * @return  array
      */
-    public function &getData()
+    public function &getData(): array
     {
         return $this->_data;
     }
 
     /**
      * Accept a visitor.
-     *
-     * @param   \Hoa\Visitor\Visit  $visitor    Visitor.
-     * @param   mixed               &$handle    Handle (reference).
-     * @param   mixed               $eldnah     Handle (no reference).
-     * @return  mixed
      */
     public function accept(
         Visitor\Visit $visitor,
@@ -348,8 +298,6 @@ public function accept(
 
     /**
      * Remove circular reference to the parent (help the garbage collector).
-     *
-     * @return  void
      */
     public function __destruct()
     {
diff --git a/Visitor/Dump.php b/Source/Visitor/Dump.php
similarity index 87%
rename from Visitor/Dump.php
rename to Source/Visitor/Dump.php
index f739b8b2..68d851e2 100644
--- a/Visitor/Dump.php
+++ b/Source/Visitor/Dump.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,9 +44,6 @@
  * Class \Hoa\Compiler\Visitor\Dump.
  *
  * Dump AST produced by LL(k) compiler.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Dump implements Visitor\Visit
 {
@@ -59,11 +58,6 @@ class Dump implements Visitor\Visit
 
     /**
      * Visit an element.
-     *
-     * @param   \Hoa\Visitor\Element  $element    Element to visit.
-     * @param   mixed                 &$handle    Handle (reference).
-     * @param   mixed                 $eldnah     Handle (not reference).
-     * @return  mixed
      */
     public function visit(
         Visitor\Element $element,
@@ -103,11 +97,8 @@ public function visit(
 
     /**
      * Dump data.
-     *
-     * @param   mixed  $data    Data.
-     * @return  string
      */
-    protected function dumpData($data)
+    protected function dumpData($data): ?string
     {
         $out = null;
 
diff --git a/Test/Integration/Documentation.php b/Test/Integration/Documentation.php
index a8b80b1e..11c0ab91 100644
--- a/Test/Integration/Documentation.php
+++ b/Test/Integration/Documentation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Integration\Documentation.
  *
  * Test suite of the examples in the documentation.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Documentation extends Test\Integration\Suite implements Test\Decorrelated
 {
diff --git a/Test/Integration/Llk/Documentation.php b/Test/Integration/Llk/Documentation.php
index e50a3e22..5f945b01 100644
--- a/Test/Integration/Llk/Documentation.php
+++ b/Test/Integration/Llk/Documentation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Integration\Documentation.
  *
  * Test suite of the examples in the documentation.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Documentation extends Test\Integration\Suite implements Test\Decorrelated
 {
diff --git a/Test/Integration/Llk/Rule/Analyzer.php b/Test/Integration/Llk/Rule/Analyzer.php
index 4d191727..19b764b6 100644
--- a/Test/Integration/Llk/Rule/Analyzer.php
+++ b/Test/Integration/Llk/Rule/Analyzer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -45,9 +47,6 @@
  * Class \Hoa\Compiler\Test\Integration\Llk\Rule\Analyzer.
  *
  * Test suite of the rule analyzer.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Analyzer extends Test\Integration\Suite
 {
diff --git a/Test/Integration/Llk/Soundness.php b/Test/Integration/Llk/Soundness.php
index 76795fdd..cb33fa03 100644
--- a/Test/Integration/Llk/Soundness.php
+++ b/Test/Integration/Llk/Soundness.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -42,9 +44,6 @@
  * Class \Hoa\Compiler\Test\Integration\Llk\Soundness.
  *
  * Check soundness of the LL(k) compiler.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Soundness extends Json\Test\Integration\Soundness
 {
diff --git a/Test/Unit/Exception/Exception.php b/Test/Unit/Exception/Exception.php
index 8a480ba8..e6845a91 100644
--- a/Test/Unit/Exception/Exception.php
+++ b/Test/Unit/Exception/Exception.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\Exception.
  *
  * Test suite of the exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Exception extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Exception/FinalStateHasNotBeenReached.php b/Test/Unit/Exception/FinalStateHasNotBeenReached.php
index 54ada138..e042804e 100644
--- a/Test/Unit/Exception/FinalStateHasNotBeenReached.php
+++ b/Test/Unit/Exception/FinalStateHasNotBeenReached.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\FinalStateHasNotBeenReached.
  *
  * Test suite of the lexer state exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class FinalStateHasNotBeenReached extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Exception/IllegalToken.php b/Test/Unit/Exception/IllegalToken.php
index 1d22e8a3..eb39bd2d 100644
--- a/Test/Unit/Exception/IllegalToken.php
+++ b/Test/Unit/Exception/IllegalToken.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\IllegalToken.
  *
  * Test suite of the illegal token exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class IllegalToken extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Exception/Lexer.php b/Test/Unit/Exception/Lexer.php
index fc7309a5..7983ac64 100644
--- a/Test/Unit/Exception/Lexer.php
+++ b/Test/Unit/Exception/Lexer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\Lexer.
  *
  * Test suite of the lexer exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Lexer extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Exception/Rule.php b/Test/Unit/Exception/Rule.php
index bf899856..c81f9a04 100644
--- a/Test/Unit/Exception/Rule.php
+++ b/Test/Unit/Exception/Rule.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\Rule.
  *
  * Test suite of the rule exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Rule extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Exception/UnexpectedToken.php b/Test/Unit/Exception/UnexpectedToken.php
index 2e3d9f80..29224a1c 100644
--- a/Test/Unit/Exception/UnexpectedToken.php
+++ b/Test/Unit/Exception/UnexpectedToken.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\UnexpectedToken.
  *
  * Test suite of the unexpected token exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class UnexpectedToken extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Exception/UnrecognizedToken.php b/Test/Unit/Exception/UnrecognizedToken.php
index 43bfede1..90205e4f 100644
--- a/Test/Unit/Exception/UnrecognizedToken.php
+++ b/Test/Unit/Exception/UnrecognizedToken.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Exception\UnrecognizedToken.
  *
  * Test suite of the unrecognized token exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class UnrecognizedToken extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Lexer.php b/Test/Unit/Llk/Lexer.php
index 58a93f14..601f162c 100644
--- a/Test/Unit/Llk/Lexer.php
+++ b/Test/Unit/Llk/Lexer.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Lexer.
  *
  * Test suite of the lexer class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Lexer extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Llk.php b/Test/Unit/Llk/Llk.php
index 79db49d9..c8d7497c 100644
--- a/Test/Unit/Llk/Llk.php
+++ b/Test/Unit/Llk/Llk.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -45,9 +47,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Llk.
  *
  * Test suite of the LL(k) helper class.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Llk extends Test\Unit\Suite
 {
@@ -104,7 +103,7 @@ public function case_save()
     {
         $this
             ->given(
-                $stream = new File\Read('hoa://Library/Compiler/Llk/Llk.pp'),
+                $stream = new File\Read('hoa://Library/Compiler/Source/Llk/Llk.pp'),
                 $parser = SUT::load($stream)
             )
             ->when($result = SUT::save($parser, 'Foobar'))
diff --git a/Test/Unit/Llk/Rule/Choice.php b/Test/Unit/Llk/Rule/Choice.php
index a2ba2211..8fe8a546 100644
--- a/Test/Unit/Llk/Rule/Choice.php
+++ b/Test/Unit/Llk/Rule/Choice.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Choice.
  *
  * Test suite of the choice rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Choice extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Rule/Concatenation.php b/Test/Unit/Llk/Rule/Concatenation.php
index 8a7d44d6..32042e2e 100644
--- a/Test/Unit/Llk/Rule/Concatenation.php
+++ b/Test/Unit/Llk/Rule/Concatenation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Concatenation.
  *
  * Test suite of the concatenation rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Concatenation extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Rule/Ekzit.php b/Test/Unit/Llk/Rule/Ekzit.php
index d7d98e30..a05d7a02 100644
--- a/Test/Unit/Llk/Rule/Ekzit.php
+++ b/Test/Unit/Llk/Rule/Ekzit.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Ekzit.
  *
  * Test suite of the ekzit invocation.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Ekzit extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Rule/Entry.php b/Test/Unit/Llk/Rule/Entry.php
index b885e42f..38bf259c 100644
--- a/Test/Unit/Llk/Rule/Entry.php
+++ b/Test/Unit/Llk/Rule/Entry.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Entry.
  *
  * Test suite of the entry invocation.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Entry extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Rule/Invocation.php b/Test/Unit/Llk/Rule/Invocation.php
index 797f7a53..e47ed953 100644
--- a/Test/Unit/Llk/Rule/Invocation.php
+++ b/Test/Unit/Llk/Rule/Invocation.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -43,9 +45,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Invocation.
  *
  * Test suite of an invocation rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Invocation extends Test\Unit\Suite
 {
@@ -62,8 +61,8 @@ public function case_constructor()
                     ->isEqualTo($rule)
                 ->string($result->getData())
                     ->isEqualTo($data)
-                ->variable($result->getTodo())
-                    ->isNull()
+                ->array($result->getTodo())
+                    ->isEmpty()
                 ->integer($result->getDepth())
                     ->isEqualTo(-1)
                 ->boolean($result->isTransitional())
diff --git a/Test/Unit/Llk/Rule/Repetition.php b/Test/Unit/Llk/Rule/Repetition.php
index a11523da..9afdd535 100644
--- a/Test/Unit/Llk/Rule/Repetition.php
+++ b/Test/Unit/Llk/Rule/Repetition.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Repetition.
  *
  * Test suite of a repetition rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Repetition extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Rule/Rule.php b/Test/Unit/Llk/Rule/Rule.php
index 78958b92..09f40096 100644
--- a/Test/Unit/Llk/Rule/Rule.php
+++ b/Test/Unit/Llk/Rule/Rule.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -43,9 +45,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Rule.
  *
  * Test suite of a rule.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Rule extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Rule/Token.php b/Test/Unit/Llk/Rule/Token.php
index 2a66fc13..7466dc58 100644
--- a/Test/Unit/Llk/Rule/Token.php
+++ b/Test/Unit/Llk/Rule/Token.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Rule\Token.
  *
  * Test suite of a token.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Token extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/Sampler/Exception.php b/Test/Unit/Llk/Sampler/Exception.php
index d7cdf097..9d1e58f0 100644
--- a/Test/Unit/Llk/Sampler/Exception.php
+++ b/Test/Unit/Llk/Sampler/Exception.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\Sampler\Exception.
  *
  * Test suite of the sampler exception.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class Exception extends Test\Unit\Suite
 {
diff --git a/Test/Unit/Llk/TreeNode.php b/Test/Unit/Llk/TreeNode.php
index 2c911cc5..bcb25b41 100644
--- a/Test/Unit/Llk/TreeNode.php
+++ b/Test/Unit/Llk/TreeNode.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /**
  * Hoa
  *
@@ -44,9 +46,6 @@
  * Class \Hoa\Compiler\Test\Unit\Llk\TreeNode.
  *
  * Test suite of the tree node.
- *
- * @copyright  Copyright © 2007-2017 Hoa community
- * @license    New BSD License
  */
 class TreeNode extends Test\Unit\Suite
 {
diff --git a/composer.json b/composer.json
index b202433a..5e059998 100644
--- a/composer.json
+++ b/composer.json
@@ -27,23 +27,25 @@
         "source": "https://central.hoa-project.net/Resource/Library/Compiler"
     },
     "require": {
-        "php"            : ">=5.5.0",
-        "hoa/consistency": "~1.0",
-        "hoa/exception"  : "~1.0",
-        "hoa/file"       : "~1.0",
-        "hoa/iterator"   : "~2.0",
-        "hoa/math"       : "~1.0",
-        "hoa/protocol"   : "~1.0",
-        "hoa/regex"      : "~1.0",
-        "hoa/visitor"    : "~2.0"
+        "php"            : ">=7.1",
+        "hoa/consistency": "dev-master",
+        "hoa/exception"  : "dev-master",
+        "hoa/file"       : "dev-master",
+        "hoa/iterator"   : "dev-master",
+        "hoa/math"       : "dev-master",
+        "hoa/protocol"   : "dev-master",
+        "hoa/regex"      : "dev-master",
+        "hoa/visitor"    : "dev-master"
     },
     "require-dev": {
-        "hoa/json": "~2.0",
-        "hoa/test": "~2.0"
+        "hoa/json": "dev-master",
+        "hoa/test": "dev-master"
     },
     "autoload": {
         "psr-4": {
-            "Hoa\\Compiler\\": "."
+            "Hoa\\Compiler\\"      : "Source",
+            "Hoa\\Compiler\\Bin\\" : "Bin",
+            "Hoa\\Compiler\\Test\\": "Test"
         }
     },
     "extra": {