Haskell如何处理重载多态性？ [英] How does Haskell handle overloading polymorphism?

问题描述

我有一个关于Haskell多态性的问题。

据我所知，有两种类型的多态：

1. 参数：您不指定输入类型。 / p>
   
   

     functionName :: [a]  - >一个
     




2. 重载：作为命令式编程，






我的问题是：Haskell如何处理重载？

解决方案

使用类型类完成Haskell中的重载。例如，假设您要重载返回 Int 的函数 foo ：

  class Fooable a where 
 foo :: a  - > Int 
 
实例Fooable Int其中
 foo = id 
 
实例Fooable Bool其中
 foo _ = 42 
  

然而，它们比大多数语言中的重载机制更强大。例如，你可以在返回类型上重载：



  class Barable a where 
 bar :: Int  - > a 
 
实例Barable Int其中
 bar x = x + 3 
 
实例Barable Bool其中
 bar x = x < 10 
  

有关更多示例，请查看预定义的类型在Haskell中。




I have a question about Haskell polymorphism.

As I've learned, there are two types of polymorphism:

1. Parametric: where you do not specify the input type.

   Example:

   functionName :: [a] -> a
   

2. Overloading: as imperative programming, i.e. passing different arguments to the same function.

My problem is: how does Haskell handle overloading?

解决方案

Overloading in Haskell is done using type classes. For example, let's say you want to overload a function foo that returns an Int:

class Fooable a where
    foo :: a -> Int

instance Fooable Int where
    foo = id

instance Fooable Bool where
    foo _ = 42

However, they are more powerful than the overloading mechanisms found in most languages. For example, you can overload on the return type:

class Barable a where
    bar :: Int -> a

instance Barable Int where
    bar x = x + 3

instance Barable Bool where
    bar x = x < 10

For more examples, have a look at the predefined type classes in Haskell.

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