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vendor/doctrine/lexer/docs/en/simple-parser-example.rst

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+Simple Parser Example
+=====================
+
+Extend the ``Doctrine\Common\Lexer\AbstractLexer`` class and implement
+the ``getCatchablePatterns``, ``getNonCatchablePatterns``, and ``getType``
+methods. Here is a very simple example lexer implementation named ``CharacterTypeLexer``.
+It tokenizes a string to ``T_UPPER``, ``T_LOWER`` and``T_NUMBER`` tokens:
+
+.. code-block:: php
+    <?php
+
+    use Doctrine\Common\Lexer\AbstractLexer;
+
+    class CharacterTypeLexer extends AbstractLexer
+    {
+        const T_UPPER =  1;
+        const T_LOWER =  2;
+        const T_NUMBER = 3;
+
+        protected function getCatchablePatterns()
+        {
+            return array(
+                '[a-bA-Z0-9]',
+            );
+        }
+
+        protected function getNonCatchablePatterns()
+        {
+            return array();
+        }
+
+        protected function getType(&$value)
+        {
+            if (is_numeric($value)) {
+                return self::T_NUMBER;
+            }
+
+            if (strtoupper($value) === $value) {
+                return self::T_UPPER;
+            }
+
+            if (strtolower($value) === $value) {
+                return self::T_LOWER;
+            }
+        }
+    }
+
+Use ``CharacterTypeLexer`` to extract an array of upper case characters:
+
+.. code-block:: php
+    <?php
+
+    class UpperCaseCharacterExtracter
+    {
+        private $lexer;
+
+        public function __construct(CharacterTypeLexer $lexer)
+        {
+            $this->lexer = $lexer;
+        }
+
+        public function getUpperCaseCharacters($string)
+        {
+            $this->lexer->setInput($string);
+            $this->lexer->moveNext();
+
+            $upperCaseChars = array();
+            while (true) {
+                if (!$this->lexer->lookahead) {
+                    break;
+                }
+
+                $this->lexer->moveNext();
+
+                if ($this->lexer->token['type'] === CharacterTypeLexer::T_UPPER) {
+                    $upperCaseChars[] = $this->lexer->token['value'];
+                }
+            }
+
+            return $upperCaseChars;
+        }
+    }
+
+    $upperCaseCharacterExtractor = new UpperCaseCharacterExtracter(new CharacterTypeLexer());
+    $upperCaseCharacters = $upperCaseCharacterExtractor->getUpperCaseCharacters('1aBcdEfgHiJ12');
+
+    print_r($upperCaseCharacters);
+
+The variable ``$upperCaseCharacters`` contains all of the upper case
+characters:
+
+.. code-block:: php
+    Array
+    (
+        [0] => B
+        [1] => E
+        [2] => H
+        [3] => J
+    )
+
+This is a simple example but it should demonstrate the low level API
+that can be used to build more complex parsers.