Haskell 默认超类实例
我想从一些自定义类的 Num 声明中取出一些样板文件（称为单项式和多项式）。而不是写
instance Num (Monomial) where
f - g = f + (negate g)
abs _ = undefined
有没有办法解决这个问题？我遇到了 默认超类实例 和名为“strathclyde haskell 增强" 如果实现的话可能会让我写一些类似的东西，
class SimpleNum a => Num a where
(+) :: a -> a -> a -- standard ring stuff
(*) :: a -> a -> a
one :: a
zero :: a
instance Num (SimpleNum a) where
f - g = f + (negate g)
abs _ = undefined
什么是通常/简单的处理方法？
I want to take some of the boilerplate out of Num declarations for a few custom classes (call them Monomial and Polynomial). Instead of writing
instance Num (Monomial) where
f - g = f + (negate g)
abs _ = undefined
Is there a way to get around this? I came across default superclass instances and something called "the strathclyde haskell enhancement" which if implemented might let me write something like,
class SimpleNum a => Num a where
(+) :: a -> a -> a -- standard ring stuff
(*) :: a -> a -> a
one :: a
zero :: a
instance Num (SimpleNum a) where
f - g = f + (negate g)
abs _ = undefined
What's the usual / simple way of dealing with this?
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处理此问题的常用方法是至少执行以下一项或多项操作：
多发牢骚。
像这样编写辅助函数：
使用诸如 Template Haskell 之类的工具 和 派生。
尝试实现您提到的扩展。 （不幸的是，这并不像您想象的那么容易。）
The usual ways of dealing this is to do at least one or more of the following:
Grumble a lot.
Write helper functions like this:
Use tools like Template Haskell and Derive.
Attempt to implement extensions like the one you mention. (This unfortunately not as easy as you might think.)