ANTLR4 Runtime for PHP

First steps

1. Install ANTLR4

The getting started guide should get you started.

2. Install the PHP ANTLR runtime

Each target language for ANTLR has a runtime package for running parser generated by ANTLR4. The runtime provides a common set of tools for using your parser.

Install the runtime with Composer:

composer require antlr/antlr4-php-runtime

3. Generate your parser

You use the ANTLR4 "tool" to generate a parser. These will reference the ANTLR runtime, installed above.

Suppose you're using a UNIX system and have set up an alias for the ANTLR4 tool as described in the getting started guide. To generate your PHP parser, run the following command:

antlr4 -Dlanguage=PHP MyGrammar.g4

For a full list of antlr4 tool options, please visit the tool documentation page.

Complete example

Suppose you're using the JSON grammar from https://github.com/antlr/grammars-v4/tree/master/json.

Then, invoke antlr4 -Dlanguage=PHP JSON.g4. The result of this is a collection of .php files in the parser directory including:

JsonParser.php
JsonBaseListener.php
JsonLexer.php
JsonListener.php

Another common option to the ANTLR tool is -visitor, which generates a parse tree visitor, but we won't be doing that here. For a full list of antlr4 tool options, please visit the tool documentation page.

We'll write a small main func to call the generated parser/lexer (assuming they are separate). This one writes out the encountered ParseTreeContext's:

<?php

namespace JsonParser;

use Antlr\Antlr4\Runtime\CommonTokenStream;
use Antlr\Antlr4\Runtime\Error\Listeners\DiagnosticErrorListener;
use Antlr\Antlr4\Runtime\InputStream;
use Antlr\Antlr4\Runtime\ParserRuleContext;
use Antlr\Antlr4\Runtime\Tree\ErrorNode;
use Antlr\Antlr4\Runtime\Tree\ParseTreeListener;
use Antlr\Antlr4\Runtime\Tree\ParseTreeWalker;
use Antlr\Antlr4\Runtime\Tree\TerminalNode;

final class TreeShapeListener implements ParseTreeListener {
    public function visitTerminal(TerminalNode $node) : void {}
    public function visitErrorNode(ErrorNode $node) : void {}
    public function exitEveryRule(ParserRuleContext $ctx) : void {}

    public function enterEveryRule(ParserRuleContext $ctx) : void {
        echo $ctx->getText();
    }
}

$input = InputStream::fromPath($argv[1]);
$lexer = new JSONLexer($input);
$tokens = new CommonTokenStream($lexer);
$parser = new JSONParser($tokens);
$parser->addErrorListener(new DiagnosticErrorListener());
$tree = $parser->json();

ParseTreeWalker::default()->walk(new TreeShapeListener(), $tree);

Create a example.json file:

{"a":1}

Parse the input file:

php json.php example.json

The expected output is:

{"a":1}
{"a":1}
"a":1
1