Rechenbeispiel mit Klammern

<?php
global $pre, $suff;
$pre = "#(?<![0-9])([-+]?([0-9]*\.[0-9]+|[0-9]+))(([";
$suff = "])([-+]?([0-9]*\.[0-9]+|[0-9]+)))+#";

function replace_bracket($input) {
    global $pre,$suff;
    $operations = array("/", "*", "-", "+");
    $result = $input;
    if(is_array($input)) {
        $result = $input[1];
    }
    foreach($operations as $op) {
        $result = preg_replace_callback($pre.$op.$suff, 'replace_math' ,$result);
    }
    return $result;
}

function replace_math($matches) {
    if ($matches[4] == '-') {
        $vals = explode('!', preg_replace('/(--)*-(-?)/', '!$2', $matches[0]));
    }else {
        $vals = explode($matches[4], $matches[0]);
    }
    switch($matches[4]) {
        case '*':
            return array_product($vals);
        case '/':
            $result = array_shift($vals);
            foreach($vals as $val) {$result/=$val;}
            return $result;
        case '+':
            return array_sum($vals);
        case '-':
            return array_shift($vals)-array_sum($vals);
    }
}

$mathString = "(3+4-5.5*3)*-20/(5+81-3)-5+4*-3.141529*-10";
$result = $mathString;
while(strpos($result,"(")!== false) {
    $result = preg_replace_callback('/\\(([^()]*)\\)/', 'replace_bracket', $result);
}
$result = replace_bracket($result);
eval('$phpResult = '.$mathString.';');
echo $phpResult. " == ".$result;