DesignPatternsPHP/DesignPatternsPHP · error · Exception

no exist variable: $name

Error message

no exist variable: $name

What it means

Context::lookUp() is the Interpreter pattern's variable lookup. It throws a generic Exception when the requested variable name is not present in the context's variable pool, because evaluating a TerminalExpression for an unassigned variable has no defined value.

Source

Thrown at Behavioral/Interpreter/Context.php:16

<?php

declare(strict_types=1);

namespace DesignPatterns\Behavioral\Interpreter;

use Exception;

class Context
{
    private array $poolVariable;

    public function lookUp(string $name): bool
    {
        if (!key_exists($name, $this->poolVariable)) {
            throw new Exception("no exist variable: $name");
        }

        return $this->poolVariable[$name];
    }

    public function assign(VariableExp $variable, bool $val)
    {
        $this->poolVariable[$variable->getName()] = $val;
    }
}

View on GitHub (pinned to 54254e0f2a)

Solutions

1. Call $context->assign(new VariableExp('name'), true) before evaluating expressions that reference 'name'
2. Verify the variable name string matches exactly (case-sensitive) between the expression and the assignment
3. Reuse the same Context instance across expression construction and evaluation

Example fix

// before
$context->lookUp('x'); // throws: no exist variable: x
// after
$context->assign(new VariableExp('x'), true);
$context->lookUp('x');

$vars = (new ReflectionObject($context))->getProperty('poolVariable')->getValue($context);
if (!array_key_exists('x', $vars)) { $context->assign(new VariableExp('x'), true); }

function hasVariable(Context $context, string $name): bool {
    $prop = new ReflectionObject($context)->getProperty('poolVariable');
    $prop->setAccessible(true);
    return array_key_exists($name, $prop->getValue($context));
}

try {
    $value = $context->lookUp('x');
} catch (Exception $e) {
    $value = false; // default for unassigned variable
}

When it happens

Trigger: Calling Context::lookUp('name') before Context::assign() was called for that VariableExp; a misspelled variable name in an expression; evaluating an expression tree against a fresh/empty Context.

Common situations: Building interpreter expressions in the wrong order (evaluating before assignments), reusing a new Context object with expressions that reference variables set on an older Context, or typos in variable names.

Related errors

• Invalid state given
• Cannot unserialize singleton
• Unknown format given
• Invalid PostId given
• Invalid state given!

AI-assisted analysis of DesignPatternsPHP/DesignPatternsPHP@54254e0f2a (2026-09-01). Data as JSON: /api/errors/91193f3fadb29ef0. Report an issue: GitHub.