Haskell难以使用变量的类型签名

Question

tuple :: (Integer a,Fractional b) => (a,b,String)
tuple = (18,5.55,"Charana")

所以这给了我错误

‘Integer’ is applied to too many type arguments
In the type signature for ‘tuple’:
tuple :: (Integer a, Fractional b) => (a, b, String)

为什么会这样？

Answer 1

Integer是Haskell中的具体类型，而Integral是一个类型类，用于表示可以表示为整数的事物。因此，您可以选择写：

tuple :: Fractional a => (Integer,a,String)
tuple = (18,5.55,"Charana")

或

tuple :: (Integral a,Fractional b) => (a,b,String)
tuple = (18,5.55,"Charana")

Answer 2

Integer只是一种类型。

tuple :: Fractional a => (Integer, a, String)

或许您打算使用Integral a？