haskell - 将 float 转换为整数

Question

我正在尝试定义:

square :: Integer -> Integer 
square = round . (** 2)

我得到:

<interactive>:9:9: error:
    • No instance for (RealFrac Integer) arising from a use of ‘round’
    • In the first argument of ‘(.)’, namely ‘round’
      In the expression: round . (** 2)
      In an equation for ‘square’: square = round . (** 2)

<interactive>:9:18: error:
    • No instance for (Floating Integer)
        arising from an operator section
    • In the second argument of ‘(.)’, namely ‘(** 2)’
      In the expression: round . (** 2)
      In an equation for ‘square’: square = round . (** 2)

我还是这门语言的新手，我似乎无法将 Floating 的实例转换为 Integer。有人知道我该怎么做吗？

Answer 1

Haskell 有多个不同类型的指数函数:

• (^) :: (Num a, Integral b) => a -> b -> a
• (^^) :: (Fractional a, Integral b) => a -> b -> a
• (**) :: Floating a => a -> a -> a

您要找的就是(^)。有了它，你甚至不需要round:

square :: Integer -> Integer 
square = (^ 2)