我如何在Haskell中编写符号的限定名称？ [英] How do I write the qualified name of a symbol in Haskell?

问题描述

我想要使用相同的中缀运算符（<> ）的两个不同Haskell模块之间发生名称冲突。 Haskell 98报告称，

I've got a name clash between two different Haskell modules that want to use the same infix operator (<*>). The Haskell 98 report says that

modid.varsym

是允许的，但我无法让它工作。在这里完整的是 Test.hs ：

is permitted, but I can't get it to work. In their entirety here are Test.hs:

module Test
where

import qualified Test2 as T

three = T.<*>

和 Test2.hs ：

module Test2
where
(<*>) = 3

但试图编译错误信息的结果：

But trying to compile results in an error message:

Test.hs:6:12: parse error on input `T.<*>'

我试过 T。（*），但这也不管用。

I tried T.(<*>) but that doesn't work either.

如何引用由导入限定？

推荐答案

three = (T.<*>)

将中缀运算符定义为整数是奇怪的。让我们考虑 \\ （设置差异运算符）：

It's weird to define an infix operator as an integer. Let's consider \\ (the set difference operator):

import qualified Data.List as L

foo = [1..5] L.\\ [1..3] -- evaluates to [4,5]
diff = (L.\\)

如上所示， L 。\\ 是一个合格的中缀操作符;它仍然是一个中缀运算符。要将它用作值，你需要在整个事物中放置括号。

As you can see above, L.\\ is a qualified infix operator; and it still works as an infix operator. To use it as a value, you put parentheses around the whole thing.

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