如何使用值构造函数在PureScript中创建记录

Question

我试图基于数据数组创建记录，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，我试图使用Address值构造函数创建Address类型的Record，但是在编译时会引发错误：

Unknown data constructor Address

Answer 1

type只定义类型别名，所以Address和

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

实际上是同一类型。如果要生成构造函数，则必须使用newtype：

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

或者，您可以在代码中摆脱构造函数，而只使用记录类型：

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