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Dumping and Manipulating the AST of Expressions

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Dumping and Manipulating the AST of Expressions

Manipulating or inspecting the expressions created with the ExpressionLanguage component is difficult because they 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 getNodes() method after parsing any expression to get its AST:

use Symfony\Component\ExpressionLanguage\ExpressionLanguage;

$ast = (new ExpressionLanguage())
    ->parse('1 + 2', array())
    ->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 toArray() method to turn the AST into an array:

// ...

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

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.