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Kevin Adametz 2020-07-09 12:49:32 +02:00
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DQL Lexer
=========
Here is a more complicated example from the Doctrine ORM project.
The ``Doctrine\ORM\Query\Lexer`` implementation for DQL looks something
like the following:
.. code-block:: php
use Doctrine\Common\Lexer\AbstractLexer;
class Lexer extends AbstractLexer
{
// All tokens that are not valid identifiers must be < 100
public const T_NONE = 1;
public const T_INTEGER = 2;
public const T_STRING = 3;
public const T_INPUT_PARAMETER = 4;
public const T_FLOAT = 5;
public const T_CLOSE_PARENTHESIS = 6;
public const T_OPEN_PARENTHESIS = 7;
public const T_COMMA = 8;
public const T_DIVIDE = 9;
public const T_DOT = 10;
public const T_EQUALS = 11;
public const T_GREATER_THAN = 12;
public const T_LOWER_THAN = 13;
public const T_MINUS = 14;
public const T_MULTIPLY = 15;
public const T_NEGATE = 16;
public const T_PLUS = 17;
public const T_OPEN_CURLY_BRACE = 18;
public const T_CLOSE_CURLY_BRACE = 19;
// All tokens that are identifiers or keywords that could be considered as identifiers should be >= 100
public const T_ALIASED_NAME = 100;
public const T_FULLY_QUALIFIED_NAME = 101;
public const T_IDENTIFIER = 102;
// All keyword tokens should be >= 200
public const T_ALL = 200;
public const T_AND = 201;
public const T_ANY = 202;
public const T_AS = 203;
public const T_ASC = 204;
public const T_AVG = 205;
public const T_BETWEEN = 206;
public const T_BOTH = 207;
public const T_BY = 208;
public const T_CASE = 209;
public const T_COALESCE = 210;
public const T_COUNT = 211;
public const T_DELETE = 212;
public const T_DESC = 213;
public const T_DISTINCT = 214;
public const T_ELSE = 215;
public const T_EMPTY = 216;
public const T_END = 217;
public const T_ESCAPE = 218;
public const T_EXISTS = 219;
public const T_FALSE = 220;
public const T_FROM = 221;
public const T_GROUP = 222;
public const T_HAVING = 223;
public const T_HIDDEN = 224;
public const T_IN = 225;
public const T_INDEX = 226;
public const T_INNER = 227;
public const T_INSTANCE = 228;
public const T_IS = 229;
public const T_JOIN = 230;
public const T_LEADING = 231;
public const T_LEFT = 232;
public const T_LIKE = 233;
public const T_MAX = 234;
public const T_MEMBER = 235;
public const T_MIN = 236;
public const T_NEW = 237;
public const T_NOT = 238;
public const T_NULL = 239;
public const T_NULLIF = 240;
public const T_OF = 241;
public const T_OR = 242;
public const T_ORDER = 243;
public const T_OUTER = 244;
public const T_PARTIAL = 245;
public const T_SELECT = 246;
public const T_SET = 247;
public const T_SOME = 248;
public const T_SUM = 249;
public const T_THEN = 250;
public const T_TRAILING = 251;
public const T_TRUE = 252;
public const T_UPDATE = 253;
public const T_WHEN = 254;
public const T_WHERE = 255;
public const T_WITH = 256;
/**
* Creates a new query scanner object.
*
* @param string $input A query string.
*/
public function __construct($input)
{
$this->setInput($input);
}
/**
* {@inheritdoc}
*/
protected function getCatchablePatterns()
{
return [
'[a-z_][a-z0-9_]*\:[a-z_][a-z0-9_]*(?:\\\[a-z_][a-z0-9_]*)*', // aliased name
'[a-z_\\\][a-z0-9_]*(?:\\\[a-z_][a-z0-9_]*)*', // identifier or qualified name
'(?:[0-9]+(?:[\.][0-9]+)*)(?:e[+-]?[0-9]+)?', // numbers
"'(?:[^']|'')*'", // quoted strings
'\?[0-9]*|:[a-z_][a-z0-9_]*', // parameters
];
}
/**
* {@inheritdoc}
*/
protected function getNonCatchablePatterns()
{
return ['\s+', '(.)'];
}
/**
* {@inheritdoc}
*/
protected function getType(&$value)
{
$type = self::T_NONE;
switch (true) {
// Recognize numeric values
case (is_numeric($value)):
if (strpos($value, '.') !== false || stripos($value, 'e') !== false) {
return self::T_FLOAT;
}
return self::T_INTEGER;
// Recognize quoted strings
case ($value[0] === "'"):
$value = str_replace("''", "'", substr($value, 1, strlen($value) - 2));
return self::T_STRING;
// Recognize identifiers, aliased or qualified names
case (ctype_alpha($value[0]) || $value[0] === '_' || $value[0] === '\\'):
$name = 'Doctrine\ORM\Query\Lexer::T_' . strtoupper($value);
if (defined($name)) {
$type = constant($name);
if ($type > 100) {
return $type;
}
}
if (strpos($value, ':') !== false) {
return self::T_ALIASED_NAME;
}
if (strpos($value, '\\') !== false) {
return self::T_FULLY_QUALIFIED_NAME;
}
return self::T_IDENTIFIER;
// Recognize input parameters
case ($value[0] === '?' || $value[0] === ':'):
return self::T_INPUT_PARAMETER;
// Recognize symbols
case ($value === '.'):
return self::T_DOT;
case ($value === ','):
return self::T_COMMA;
case ($value === '('):
return self::T_OPEN_PARENTHESIS;
case ($value === ')'):
return self::T_CLOSE_PARENTHESIS;
case ($value === '='):
return self::T_EQUALS;
case ($value === '>'):
return self::T_GREATER_THAN;
case ($value === '<'):
return self::T_LOWER_THAN;
case ($value === '+'):
return self::T_PLUS;
case ($value === '-'):
return self::T_MINUS;
case ($value === '*'):
return self::T_MULTIPLY;
case ($value === '/'):
return self::T_DIVIDE;
case ($value === '!'):
return self::T_NEGATE;
case ($value === '{'):
return self::T_OPEN_CURLY_BRACE;
case ($value === '}'):
return self::T_CLOSE_CURLY_BRACE;
// Default
default:
// Do nothing
}
return $type;
}
}
This is roughly what the DQL Parser looks like that uses the above
Lexer implementation:
.. note::
You can see the full implementation `here <https://github.com/doctrine/doctrine2/blob/master/lib/Doctrine/ORM/Query/Parser.php>`_.
.. code-block:: php
class Parser
{
private $lexer;
public function __construct($dql)
{
$this->lexer = new Lexer();
$this->lexer->setInput($dql);
}
// ...
public function getAST()
{
// Parse & build AST
$AST = $this->QueryLanguage();
// ...
return $AST;
}
public function QueryLanguage()
{
$this->lexer->moveNext();
switch ($this->lexer->lookahead['type']) {
case Lexer::T_SELECT:
$statement = $this->SelectStatement();
break;
case Lexer::T_UPDATE:
$statement = $this->UpdateStatement();
break;
case Lexer::T_DELETE:
$statement = $this->DeleteStatement();
break;
default:
$this->syntaxError('SELECT, UPDATE or DELETE');
break;
}
// Check for end of string
if ($this->lexer->lookahead !== null) {
$this->syntaxError('end of string');
}
return $statement;
}
// ...
}
Now the AST is used to transform the DQL query in to portable SQL for whatever relational
database you are using!
.. code-block:: php
$parser = new Parser('SELECT u FROM User u');
$AST = $parser->getAST(); // returns \Doctrine\ORM\Query\AST\SelectStatement
What is an AST?
===============
AST stands for `Abstract syntax tree <http://en.wikipedia.org/wiki/Abstract_syntax_tree>`_.
In computer science, an abstract syntax tree (AST), or just syntax tree, is a
tree representation of the abstract syntactic structure of source code written
in a programming language. Each node of the tree denotes a construct occurring in
the source code.

53
vendor/doctrine/lexer/docs/en/index.rst vendored Normal file
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Introduction
============
Doctrine Lexer is a library that can be used in Top-Down, Recursive
Descent Parsers. This lexer is used in Doctrine Annotations and in
Doctrine ORM (DQL).
To write your own parser you just need to extend ``Doctrine\Common\Lexer\AbstractLexer``
and implement the following three abstract methods.
.. code-block:: php
/**
* Lexical catchable patterns.
*
* @return array
*/
abstract protected function getCatchablePatterns();
/**
* Lexical non-catchable patterns.
*
* @return array
*/
abstract protected function getNonCatchablePatterns();
/**
* Retrieve token type. Also processes the token value if necessary.
*
* @param string $value
* @return integer
*/
abstract protected function getType(&$value);
These methods define the `lexical <http://en.wikipedia.org/wiki/Lexical_analysis>`_
catchable and non-catchable patterns and a method for returning the
type of a token and filtering the value if necessary.
The Lexer is responsible for giving you an API to walk across a
string one character at a time and analyze the type of each character, value and position of
each token in the string. The low level API of the lexer is pretty simple:
- ``setInput($input)`` - Sets the input data to be tokenized. The Lexer is immediately reset and the new input tokenized.
- ``reset()`` - Resets the lexer.
- ``resetPeek()`` - Resets the peek pointer to 0.
- ``resetPosition($position = 0)`` - Resets the lexer position on the input to the given position.
- ``isNextToken($token)`` - Checks whether a given token matches the current lookahead.
- ``isNextTokenAny(array $tokens)`` - Checks whether any of the given tokens matches the current lookahead.
- ``moveNext()`` - Moves to the next token in the input string.
- ``skipUntil($type)`` - Tells the lexer to skip input tokens until it sees a token with the given value.
- ``isA($value, $token)`` - Checks if given value is identical to the given token.
- ``peek()`` - Moves the lookahead token forward.
- ``glimpse()`` - Peeks at the next token, returns it and immediately resets the peek.

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.. toctree::
:depth: 3
index
simple-parser-example
dql-parser

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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.