haskell - 为什么 Haskell/GHC 不支持记录名重载

Question

我是一个 Haskell 新手。我注意到 Haskell 不支持记录名称重载:

-- Records.hs

data Employee = Employee
  { firstName :: String
  , lastName :: String
  , ssn :: String
  } deriving (Show, Eq)

data Manager = Manager
  { firstName :: String
  , lastName :: String
  , ssn :: String
  , subordinates :: [Employee]
  } deriving (Show, Eq)

当我编译这个时，我得到:

[1 of 1] Compiling Main             ( Records.hs, Records.o )

Records.hs:10:5:
    Multiple declarations of `firstName'
    Declared at: Records.hs:4:5
                 Records.hs:10:5

Records.hs:11:5:
    Multiple declarations of `lastName'
    Declared at: Records.hs:5:5
                 Records.hs:11:5

Records.hs:12:5:
    Multiple declarations of `ssn'
    Declared at: Records.hs:6:5
                 Records.hs:12:5

鉴于 Haskell 类型系统的“强度”，编译器似乎应该很容易确定要访问哪个字段

emp = Employee "Joe" "Smith" "111-22-3333"
man = Manager "Mary" "Jones" "333-22-1111" [emp]
firstName man
firstName emp

是否有一些我没有看到的问题。我知道 Haskell 报告不允许这样做，但为什么不呢？

Answer 1

历史原因。有have been many competing designs为 Haskell 提供更好的记录系统——事实上，no consensus可以到达。然而。