Dumping and Manipulating the AST of Expressions

It’s difficult to manipulate or inspect the expressions created with the ExpressionLanguage component, because the expressions are plain strings. A better approach is to turn those expressions into an AST. In computer science, AST (Abstract Syntax Tree) is “a tree representation of the structure of source code written in a programming language”. In Symfony, a ExpressionLanguage AST is a set of nodes that contain PHP classes representing the given expression.

Dumping the AST

Call the :method:`Symfony\\Component\\ExpressionLanguage\\ExpressionLanguage::getNodes` method after parsing any expression to get its AST:

use Symfony\Component\ExpressionLanguage\ExpressionLanguage;

$ast = (new ExpressionLanguage())
    ->parse('1 + 2', [])
    ->getNodes()
;

// dump the AST nodes for inspection
var_dump($ast);

// dump the AST nodes as a string representation
$astAsString = $ast->dump();

Manipulating the AST

The nodes of the AST can also be dumped into a PHP array of nodes to allow manipulating them. Call the :method:`Symfony\\Component\\ExpressionLanguage\\ExpressionLanguage::toArray` method to turn the AST into an array:

// ...

$astAsArray = (new ExpressionLanguage())
    ->parse('1 + 2', [])
    ->getNodes()
    ->toArray()
;