adt - 如何使用 Value 构造函数在 PureScript 中创建记录

Question

我正在尝试根据数据数组创建一条记录，该函数如下所示:

type Address = {
  street :: String,
  city :: String,
  state :: String
}

convertToAddress :: Array String -> Maybe Address
convertToAddress [street, city, state] = Just (Address { street: street, city: city, state: state })
convertToAddress _ = Nothing

在这里，我尝试使用 Address 值构造函数创建 Address 类型的记录，但在编译时会抛出错误:

Unknown data constructor Address

Answer 1

type 仅定义类型别名，因此 Address 和

{
  street :: String,
  city :: String,
  state :: String
}

实际上是同一类型。如果你想生成一个构造函数，你必须使用newtype:

newtype Address = Address {
  street :: String,
  city :: String,
  state :: String
}

或者，您可以删除代码中的构造函数并仅使用记录类型:

convertToAddress :: Array String -> Maybe Address
convertToAddress [street, city, state] = Just { street: street, city: city, state: state }
convertToAddress _ = Nothing