我如何在Haskell中创建运算符？ [英] How do I create an operator in Haskell?

问题描述

制作一个三元逻辑表，我想为我称之为< => 的操作符创建自己的函数。

所以，例如，我想这样做，但这是不对的。什么是正确的做法？

 数据Ternary = T | F | M 
导出（Eq，Show，Ord）
 
 => = ::三元 - >三元 - >三元
< => T F = F 
< => T T = T 
< => T M = M 
 = F F = T 
< => F T = F 
< => F M = M 
< => M F = M 
< => M T = M 
< => MM = T 
  

解决方案

/ p>

 （< =>）:: Ternary  - >三元 - > （=）TF = F 
（=）TT = T 
（=）TM = M 
（< => = =）F F = F 
（=）FM = M 
（=）MF = M $ b = b $ b（=>）MT = M 
（=>）MM = T 
  

这将它从中缀形式转换为前缀形式。或者，您可以在定义中使用中缀：

 （< =>）:: Ternary  - >三元 - >三元
 T => F = F 
 T => T = T 
 T => M = M 
 F< => F = T 
 F< => T = F 
 F< => M = M 
 M => F = M 
 M => T = M 
 M => M = T 
  

Making a ternary logic table, and I would like to make my own function for an operator that I'll call <=>.

So, for example, I want to do this, but that isn't right. what's the correct way to do this?

data Ternary = T | F | M
deriving (Eq,  Show, Ord)

<=> :: Ternary -> Ternary -> Ternary
<=> T F = F
<=> T T = T
<=> T M = M
<=> F F = T
<=> F T = F
<=> F M = M
<=> M F = M
<=> M T = M
<=> M M = T

解决方案

Just add parentheses around your operator:

(<=>) :: Ternary -> Ternary -> Ternary
(<=>) T F = F
(<=>) T T = T
(<=>) T M = M
(<=>) F F = T
(<=>) F T = F
(<=>) F M = M
(<=>) M F = M
(<=>) M T = M
(<=>) M M = T

This turns it from infix form to prefix form. Alternatively, you can just use infix in the definition:

(<=>) :: Ternary -> Ternary -> Ternary
T <=> F = F
T <=> T = T
T <=> M = M
F <=> F = T
F <=> T = F
F <=> M = M
M <=> F = M
M <=> T = M
M <=> M = T

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