Code Delegation

You can tell the compiler which php class to include the desired grammar rule using keyword -> after name of rule definition. In this case, each processed rule will create an instance of target class (or code).

Delegate

For example every "Digit" rule must be represented as an instance of ExampleAstNode class, and all children (the result of execution) will be passed to the constructor arguments.

#Digit -> ExampleAstNode
  : <T_DIGIT> 
  ;

In this case, the rule class can look like this:

<?php

use Phplrt\Contracts\Ast\NodeInterface;
use Phplrt\Contracts\Lexer\TokenInterface;

class ExampleAstNode implements NodeInterface
{
    private int $digit;

    public function __construct($state, TokenInterface $digit, int $offset) 
    {
        $this->digit = (int)$digit->getValue();
    }

    /**
     * The required method of NodeInterface, which should return 
     * children AST nodes.
     * 
     * In this case, the node is empty, so the iterator returns nothing.
     * 
     * @return \Traversable|NodeInterface[]
     */
    public function getIterator(): \Traversable
    {
        return new \EmptyIterator();
    }
}

PHP Code

Alternatively, you can use a real PHP code inside block { ... } constructions. The result (meaning of expression return XXX) can be an any PHP value except null.

#Digit -> {
    var_dump($children);

    return new ExampleAstNode($children->getName());
}
  : <T_DIGIT> 
  ;

Note the use of the $children variable. The following variables are available inside each block:

• $ctx - Contains an object (an instance of Phplrt\Parser\ContextInterface) of the current context of program execution.

• $children - Contains the result of executing child rules (except null value).

• $file - The source/file object (instance of Phplrt\Contracts\Source\ReadableInterface) that is currently being processed by the parser.

• $source - Same with $file.

• $offset - The current offset (in bytes) relative to the beginning of the file that the parser is currently processing.

• $token - The current token (instance of Phplrt\Contracts\Lexer\TokenInterface) that is currently being processed by the parser.

• $state - The current parser's state.

• $rule - The rule (instance of Phplrt\Contracts\Grammar\RuleInterface) that is currently being processed by the parser.