Leafo\ScssPhp\Compiler::libIndex PHP Method

    protected function libIndex($args)
    {
        list($list, $value) = $args;
        if ($value[0] === Type::T_MAP) {
            return static::$null;
        }
        if ($list[0] === Type::T_MAP || $list[0] === Type::T_STRING || $list[0] === Type::T_KEYWORD || $list[0] === Type::T_INTERPOLATE) {
            $list = $this->coerceList($list, ' ');
        }
        if ($list[0] !== Type::T_LIST) {
            return static::$null;
        }
        $values = [];
        foreach ($list[2] as $item) {
            $values[] = $this->normalizeValue($item);
        }
        $key = array_search($this->normalizeValue($value), $values);
        return false === $key ? static::$null : $key + 1;
    }