A more reliable method to serialize closures.

serialization.php

<?php
/**
 * Serializes a closure as string
 * @param \Closure $closure
 * @return string
 */
function serializeClosure(\Closure $closure) {
	$ref = new ReflectionFunction($closure);
	$tokens = token_get_all(file_get_contents($ref->getFileName()));

	$tokensCount = count($tokens);
	$start = false;
	$end = $tokensCount;

	for ( $i = 0; $i < $tokensCount; ++$i ) {
		if ( is_array($tokens[$i]) && $tokens[$i][0] === T_FUNCTION && $tokens[$i][2] == $ref->getStartLine() ) {
			$start = $i;
			break;
		}
	}

	for ( $i = $start; $i < $tokensCount; ++$i ) {
		if ( is_array($tokens[$i]) && $tokens[$i][2] > $ref->getEndLine() ) {
			$end = $i - 1;
			break;
		}
	}

	$tokens = array_slice($tokens, $start, $end);

	$replaceToken = function($a) { return is_array($a) ? $a[1] : $a; };
	
	while ( count($tokens) > 0 && $tokens[0][0] === T_FUNCTION ) {

		if ( !getNesting($parameters, $tokens, '(', ')') ) // does not have parameters
			break;

		if ( !getNesting($body, $tokens, '{', '}', $parameters['end']) ) // does not have body
			break;

		if ( ($use_idx = findToken($tokens, T_USE, $parameters['end'] + 2, $body['start'] - 2)) !== false )
			getNesting($use, $tokens, '(', ')', $use_idx);

		if ( findToken($tokens, T_STRING, 0, $parameters['start']) === false ) { // is anonymous function
			while ( getNesting($tmp, $body['tokens'], T_STATIC, ';') ) {
				$tmp['start']--;
				$tmp['end']++;
				array_splice($body['tokens'], $tmp['start'], $tmp['end']);
			}

			if ( !isset($use) )
				$use = array();

			$closure = compact('parameters', 'use', 'body');

			$variables = $ref->getStaticVariables();

			$source = "return function(" . implode('', array_map($replaceToken, $closure['parameters']['tokens'])) .  ") ";
			if ( !empty($closure['use']['tokens']) ) {
				$useParams = array_map('trim', explode(',', implode('', array_map($replaceToken, $closure['use']['tokens']))));

				foreach ( $useParams as $param ) {
					if ( $param[0] == '$')
						$source = "$param = " . var_export($variables[substr($param, 1)], true) . ";\n$source";
				}

				$source .= "use(" . implode(', ', $useParams) .  ") ";
			}
				
			$source .= "{" .  implode('', array_map($replaceToken, $closure['body']['tokens'])) . "};";

			$test = function($ref) use($source) {
				$newClosure = eval($source);
				$newRef = new ReflectionFunction($newClosure);

				return ( array_map(function($a) { return $a->getName(); }, $newRef->getParameters()) == array_map(function($a) { return $a->getName(); }, $newRef->getParameters()) );
			};

			if ( $test($ref) )
				return $source;
		}
		
		$function_idx = findToken($tokens, T_FUNCTION, $body['end'] + 2);

		$tokens = $function_idx === false ? array() : array_slice($tokens, $function_idx);
	}

	return null;
}

function findToken(array $tokens, $needle, $start = 0, $end = PHP_INT_MAX)
{
  $idx = false;
	for ( $i = $start, $end = min($end, count($tokens)); $i < $end; ++$i ) {
		if ( (is_int($needle) && is_array($tokens[$i]) && $tokens[$i][0] === $needle) ||
			is_string($needle) && is_string($tokens[$i]) && $tokens[$i] === $needle ) {
			$idx = $i;
			break;
		}
	}

	return $idx;
}

function getNesting(&$matches, array $tokens, $begin = '{', $end = '}', $offset = 0)
{
	$level = 0;
	$start = false;

	for ( $i = $offset, $count = count($tokens); $i < $count; ++$i ) {
		if ( is_array($tokens[$i]) ? ($tokens[$i][0] === $begin) : ($tokens[$i] === $begin) ) {
			++$level;
			if ( $start === false )
				$start = $i + 1;
		}
		elseif ( is_array($tokens[$i]) ? ($tokens[$i][0] === $end) : ($tokens[$i] === $end) ) {
			if ( $start === false )
				break;

			if ( --$level == 0 ) {
				$matches = array(
					'tokens' => array_slice($tokens, $start, $i - $start),
					'start' => $start,
					'end' => $i - 1
				);
				return true;
			}
		}
	}

	$matches = null;
	return false;
}