如何消除选择器功能的歧义？

Question

在 GHC 8 中：

{-# LANGUAGE DuplicateRecordFields #-}

data Dog = Dog { name::String }
data Human = Human { name::String }

dog = Dog "Spike"


main = putStrLn $ name dog

此代码无法编译：

Ambiguous occurrence `name'
It could refer to either the field `name', defined at A.hs:4:22
                      or the field `name', defined at A.hs:3:18

如何正确检索我的狗的名字？

Answer 1

这应该有效：

main = putStrLn $ name (dog :: Dog)

详见DuplicateRecordFields：

Bare uses of the field refer only to the selector function, and work only if this is unambiguous.

和

However, we do not infer the type of the argument to determine the datatype, or have any way of deferring the choice to the constraint solver.

上面的例子和你的很像：

bad (p :: Person) = personId p

当范围内有另一条带有 personId 字段的记录时，这将不起作用 - 即使它看起来很明显:(

如何消除选择器功能的歧义？

How to disambiguate selector function?

haskell

ghc