“分类"在Haskell表演吗?

本文介绍了“分类"在Haskell表演吗?的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

让我说以下内容:

data Greek = Alpha | Beta | Gamma | Phi deriving Show

我想使用除Beta以外的所有项目的默认显示，我想说两个".

I want to use the default showing of all items except Beta, which I want to say "two".

我可以这样做吗?

推荐答案

deriving Show使用标准实例化机制(仅返回定义).如果您需要任何特殊的东西，则必须手动实例化它:

deriving Show uses the standard instantiation mechanism (simply returning the definition). If you want any special things, you will have to instantiate it manually:

data Greek = Alpha | Beta | Gamma | Phi instance Show Greek where show Alpha = "Alpha" show Beta = "2" show Gamma = "Gamma" show Phi = "Phi"