避免Haskell中的名称空间污染 [英] Avoiding namespace pollution in Haskell

问题描述

我在一个程序中使用了很多不同的记录，其中一些使用了相同的字段名称，例如

  data Customer = Customer {...，foo :: Int，...} 
 data Product = Product {...，foo :: Int，...} 
  

现在，访问器函数foo被定义了两次，我得到了多个声明错误。避免这种情况的一种方法是使用不同的模块进行完全限定，或者只是重新命名字段（我不想这样做）。

什么是正式提出在Haskell中处理这个问题的方法？

解决方案

这是一个非常棘手的问题。有几个提议用于修复记录系统。在相关说明中，请参阅 TDNR 和关于咖啡馆的相关讨论。

使用当前可用的语言功能，我认为最好的选择是在两个不同的模块中定义两种类型，并进行合格的导入。除此之外，如果你愿意的话，你可以实现一些类型的类机器。

在Customer.hs中

  module Customer其中
 data Customer = Customer {...，foo :: Int，...} 
  

在Product.hs中

 模块产品其中
数据Product = Product {...，foo :: Int，...} 
  

使用它们时，在Third.hs中

 模块第三个其中
 
将合格的客户导入为C 
导入限定产品为P 
 
 .. C.foo .. 
 .. P.foo .. 
  

然而，我想在你遇到递归依赖模块。

I'm using lots of different records in a program, with some of them using the same field names, e.g.

data Customer = Customer { ..., foo :: Int, ... }
data Product = Product { ..., foo :: Int, ... }

Now as the accessor function "foo" is defined twice, I get the "Multiple declarations" error. One way to avoid this would be using different modules that are imported fully qualified, or simply renaming the fields (which I don't want to do).

What is the officially suggested way of dealing with this in Haskell?

解决方案

This is a very hairy problem. There are several proposals for fixing the record system. On a related note, see TDNR and related discussion on cafe.

Using the currently available language features, I think the best option is defining the two types in two different modules, and doing a qualified import. On top of this, if you want, you can implement some type class machinery.

In Customer.hs

module Customer where
data Customer = Customer { ..., foo :: Int, ... }

In Product.hs

module Product where
data Product = Product { ..., foo :: Int, ... }

While using them, in Third.hs

module Third where

import qualified Customer as C
import qualified Product as P

.. C.foo ..
.. P.foo ..

Yet, I imagine it won't be too late before you hit the problem about recursively dependent modules.

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