View difference between Paste ID: X9XNVrDf and q5AiAzgv

 <?php
 
 function tokenize($expr) {
-	preg_match_all('/(?:-|)\d+|\+|-|\*|\/|\(|\)/', $expr, $match);
+	preg_match_all('/(?:-|)\d+|\+|-|\*|\^|\/|\(|\)/', $expr, $match);
 	$match  = $match[0];
 	$tokens = array();
 	$stack  = array();
-	$precedence = array('+' => 1, '-' => 1, '*' => 2, '/' => 2);
+	$precedence = array('+' => 2, '-' => 2, '*' => 3, '/' => 3, '^' => 4);
 
 	while($match) {
 		$token = array_shift($match);
 
 		if(is_numeric($token)) {
 			array_push($tokens, $token);
 			continue;
-		else {
+
-			if($token === ')') {
+
-				while($stack && end($stack) !== '(') {
+		if($token === ')') {
-					array_push($tokens, array_pop($stack));
+			while($stack && end($stack) !== '(') {
-				}
+
-
+
-				array_pop($stack);
+
-				continue;
+			array_pop($stack);
 			continue;
 		}
-			while($token !== '(' && ($stack && end($stack) !== '(') && $precedence[$token] < $precedence[end($stack)]) {
+
 		while($token !== '(' && ($stack && end($stack) !== '(') && $precedence[$token] < $precedence[end($stack)]) {
 			array_push($tokens, array_pop($stack));
 		}
-			array_push($stack, $token);
+
 		array_push($stack, $token);
 	}
 
 	return array_merge($tokens, array_reverse($stack));
 }
 
 function resolve($math) {
 	$funcs = array(
 		'+' => function ($left, $right) { return $left + $right; },
 		'-' => function ($left, $right) { return $left - $right; },
 		'/' => function ($left, $right) { return $left / $right; },
-		'*' => function ($left, $right) { return $left * $right; }
+		'*' => function ($left, $right) { return $left * $right; },
 		'^' => 'pow'
 	);
 
 	$stack = array();
 
 	while(count($math) > 1) {
 		$token = array_shift($math);
 
 		if(!is_numeric($token)) {
 			$token = $funcs[$token](array_shift($math), array_shift($math));
 		}
 
 		array_push($stack, $token);
 	}
 
 	return $stack[0];
 }
 
-$math = tokenize('2*3+4*(5 - 6)');
+
 $math = tokenize('3 + 4 * 2 / ( 1 - 5 ) ^ 2 ^ 3');
 echo implode(' ', $math) . PHP_EOL;
 echo resolve($math);
 
 ?>