call_user_func_array.php

<?php

if ($argc <= 3) {
    echo <<<EOI
Usage:
  % php {$argv[0]} operator arg1 arg2 [arg3 ...]
    operator    + or - or * or /
    arg         integer
EOI;
    exit;
}

$op = $argv[1];
$params = array_slice($argv, 2);
$ops = function ($op)
{
    $operators = array(
        '+' => function ($v1, $v2) { return $v1 + $v2; },
        '-' => function ($v1, $v2) { return $v1 - $v2; },
        '*' => function ($v1, $v2) { return $v1 * $v2; },
        '/' => function ($v1, $v2) { if ($v2 === 0) throw new Exception('Zero division error'); return $v1 / $v2; },
    );  
    if (!isset($operators[$op])) {
        throw new Exception('Invalid operator: operator is +, -, * or /');
    }   

    $func = $operators[$op];

    return function () use (&$func) {
        $args = func_get_args();
        $total = array_shift($args);
        foreach ($args as $arg) {
            $total = call_user_func($func, $total, (int)$arg);
        }
        return $total;
    };
};

try {
    echo call_user_func_array($ops($op), $params), PHP_EOL;
} catch (Exception $e) {
    echo $e->getMessage(), PHP_EOL;
}