Math Solver

<?php

function tokenize($expr) {
    preg_match_all('/(?:-|)\d+|\+|-|\*|\/|\(|\)/', $expr, $match);
    $match = $match[0];

    function walk(&$match) {
        $tokens = array();

        while($match) {
            $token = array_shift($match);

            if($token === ')') return $tokens;
            if($token === '(') $token = walk($match);

            array_push($tokens, $token);
        }

        return $match ? walk($match) : $tokens;
    }

    return walk($match);
}

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; }
    );

    $left  = array_shift($math);
    $op    = array_shift($math);
    $right = array_shift($math);

    $value = $funcs[$op](
        is_array($left) ? resolve($left) : $left,
        is_array($right) ? resolve($right) : $right
    );

    if(!$math) return $value;

    array_unshift($math, $value);

    return resolve($math);
}

header('content-type: text/plain');
$math = tokenize('10 + (11 - (14 / 5)) * 10');
print_r($math);
echo resolve($math);

?>