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:

1
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;
    }
}
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207

This is roughly what the DQL Parser looks like that uses the above Lexer implementation:

1
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;
    }

    // ...
}
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51

Now the AST is used to transform the DQL query in to portable SQL for whatever relational database you are using!

1
$parser = new Parser('SELECT u FROM User u');
$AST = $parser->getAST(); // returns \Doctrine\ORM\Query\AST\SelectStatement
2

What is an AST?

AST stands for 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.