是否可以在Haskell中定义一个具有两种可能类型的输入参数的函数？

Question

foo 1 2 = 1
foo 2 1 = 0
foo 'a' 'b' = -1
foo _ _ = -10

foo :: a -> a -> Int

data Bar = Int | Char
foo :: Bar -> Bar -> Int

Answer 1

你可以做

type Bar = Either Int Char

foo :: Bar -> Bar -> Int
foo (Left 1) (Left 2) = 1
foo (Right 'a') (Right 'b') = -1 
foo (Left 3) (Right 'q') = 42
foo _ _ = 10

类似的事情-要么数据类型正是为了将两种类型混合在一起。您可以滚动您自己的类似类型

data Quux = AnInt Int | AChar Char | ThreeBools Bool Bool Bool

它被称为代数数据类型。