PEG is a generic PEG parser written in PHP. This parser allows you to write parsers using the Parsing Expression Grammar.
Install PEG using Composer:
$ composer require wouterj/peg
Use the Grammar class to specify the Parsing Expression Grammar by creating
Definition instances:
use WouterJ\Peg\Grammar; use WouterJ\Peg\Definition; // specifies that Float is the main definition $grammar = new Grammar('Float', [ // matches any Digits (next definition), followed by a . (dot) and any Digits new Definition('Float', ['sequence', [ ['identifier', 'Digits'], ['literal', '.'], ['identifier', 'Digits'], ]]), // matches any Digit (next definition) one or more times new Definition('Digits', ['repeat', ['identifier', 'Digit'], 1]), // matches 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 new Definition('Digit', ['characterClass', '0-9']), ]);
Use Grammar#parse() to parse input strings using this grammar. The return value
is the part of the string that matched or null when there is no match:
// ... echo $grammar->parse('1.2'); // 1.2 echo $grammar->parse('1039.50'); // 1039.50 echo $grammar->parse('abc'); // NULL // please note that it doesn't have to match the full string echo $grammar->parse('1.2a'); // 1.2
Of course, using arrays to define the grammar is really ugly. This is why PEG
comes with PegGrammar, a parser that is able to parse PEG syntax. It returns
a ready to use grammar instance using the parsed grammar.
use WouterJ\Peg\PegGrammar; $pegGrammar = new PegGrammar(); // our float parser (equal to the previous one) $grammar = $pegGrammar->parse(<<<EOG Float <- Digits '.' Digits Digits <- Digit+ Digit <- [0-9] EOG ); $grammar->parse('1039.50'); // 1039.50
For information about the PEG syntax, see Parsing Expression Grammars: A Recognition-Based Syntactic Foundation by Bryan Ford.
The project is released under the BSD-3 Clause license. For the full copyright and license information, please view the LICENSE file that was distributed with this source code.
Whether it's just a reference, online high-five, bug report or feature proposal, all contributions are welcome. The main project is located at GitHub.