private function parseArgument($token)
    {
        $c = \count($this->arguments);

        // if input is expecting another argument, add it
        if ($this->definition->hasArgument($c)) {
            $arg = $this->definition->getArgument($c);
            $this->arguments[$arg->getName()] = $arg->isArray() ? [$token] : $token;

        // if last argument isArray(), append token to last argument
        } elseif ($this->definition->hasArgument($c - 1) && $this->definition->getArgument($c - 1)->isArray()) {
            $arg = $this->definition->getArgument($c - 1);
            $this->arguments[$arg->getName()][] = $token;

        // unexpected argument
        } else {
            $all = $this->definition->getArguments();
            if (\count($all)) {
                throw new RuntimeException(sprintf('Too many arguments, expected arguments "%s".', implode('" "', array_keys($all))));
            }

            throw new RuntimeException(sprintf('No arguments expected, got "%s".', $token));
        }
    }