The phplrt is a set of tools for programming languages recognition. The library provides lexer, parser, grammar compiler, library for working with errors, text analysis and so on.
Phplrt is available as composer repository and can be installed using the following command in a root of your project:
$ composer require phplrt/phplrtMore detailed installation instructions are here.
First, we will create the grammar for our parser.
You can read more about the grammar syntax here.
<?php
use Phplrt\Compiler\Compiler;
$compiler = new Compiler();
$compiler->load(<<<EBNF
%token T_DIGIT \d
%token T_PLUS \+
%token T_MINUS \-
%token T_POW \*
%token T_DIV /
%skip T_WHITESPACE \s+
#Expression
: <T_DIGIT> (Operator() <T_DIGIT>)*
;
#Operator
: <T_PLUS>
| <T_MINUS>
| <T_POW>
| <T_DIV>
;
EBNF);In order to quickly check the performance of what has been written, you can use
the simple parse() method. As a result, it will output the recognized abstract
syntax tree along with the predefined AST classes which can be converted to their
string representation.
<?php
echo $compiler->parse('2 + 2');
//
// Output:
//
// <Expression offset="0">
// <T_DIGIT offset="0">2</T_DIGIT>
// <Operator offset="2">
// <T_PLUS offset="2">+</T_PLUS>
// </Operator>
// <T_DIGIT offset="4">2</T_DIGIT>
// </Expression>
//After your grammar is ready and tested, it should be compiled. After that,
you no longer need the phplrt/compiler dependency (see https://phplrt.org/docs/installation#runtime-only).
file_put_contents(__DIR__ . '/grammar.php', (string)$compiler->build());This file will contain your compiled data that can be used in your custom parser.
use Phplrt\Lexer\Lexer;
use Phplrt\Parser\Parser;
use Phplrt\Parser\BuilderInterface;
use Phplrt\Parser\Context;
$data = require __DIR__ . '/grammar.php';
// Create Lexer from compiled data
$lexer = new Lexer($data['tokens']['default'], $data['skip']);
// Create Parser from compiled data
$parser = new Parser($lexer, $data['grammar'], [
// Recognition will start from the specified rule
Parser::CONFIG_INITIAL_RULE => $data['initial'],
// Rules for the abstract syntax tree builder.
// In this case, we use the data found in the compiled grammar.
Parser::CONFIG_AST_BUILDER => new class($data['reducers']) implements BuilderInterface {
public function __construct(private array $reducers) {}
public function build(Context $context, $result)
{
$state = $context->getState();
return isset($this->reducers[$state]))
? $this->reducers[$state]($context, $result)
: $result
;
}
}
]);
// Now we are ready to parse any code using the compiled grammar
$parser->parse(' ..... ');
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