public function resolve(array $shapeRef)
    {
        $shape = $shapeRef['shape'];

        if (!isset($this->definitions[$shape])) {
            throw new \InvalidArgumentException('Shape not found: ' . $shape);
        }

        $isSimple = count($shapeRef) == 1;
        if ($isSimple && isset($this->simple[$shape])) {
            return $this->simple[$shape];
        }

        $definition = $shapeRef + $this->definitions[$shape];
        $definition['name'] = $definition['shape'];
        unset($definition['shape']);

        $result = Shape::create($definition, $this);

        if ($isSimple) {
            $this->simple[$shape] = $result;
        }

        return $result;
    }