cabal（依赖）地狱背后的原因是什么？ [英] What's the reason behind cabal (dependency) hell?

问题描述

在Cabal-install中如何发生依赖关系？

我在 Cabal / Survival - HaskellWiki ：

1。 Cabal-install造成的困难是什么？

Cabal的主要困难是被称为'dependency hell'，其中
cabal-install会无法为
或其他原因安装所需的软件包，从而导致大量手动工作。作为这个难题的
例子，考虑用户希望
安装软件包A和B的情况。这两种软件都可以使用软件包C，但不能使用相同版本的C而不是
。

我明白为什么这样做通常会有意义，但不能用Cabal-install / ghc-pkg，因为您可以有多个版本安装相同的软件包。
就好像每个版本都是完全不同的软件包，在很多方面它的版本成为软件包名称的一部分（例如 mustaches-0.1 .0.0 ） - 也许它确实适用于ghc-pkg（我并不完全熟悉它，但它有道理）。

解决方案

您有这样的场景：

在B和C都依赖于A的情况下。但是，如果它们安装在不同的时间，它们可能会取决于不同的版本o例如，版本1导出类型T = Int ，但在版本2中导出 type T = Bool 。

只有当您尝试构建D时，您是否会暴露B和C针对不同版本的A构建的问题，并且您无法比较 T版本1 与 T版本2 。

How does dependency hell happen in Cabal-install?

I read the following at Cabal/Survival - HaskellWiki:

1. What is the difficulty caused by Cabal-install?

The main difficulty with Cabal is otherwise known as 'dependency hell', in which the cabal-install does not manage to install a desired package for a reason or another, leading to large amount of manual work. As an example of this difficulty, consider a case where the user wishes to install packages A and B. Both of these work with package C, but not with the same version of C.

I understand why this would make sense generally, but not with Cabal-install/ghc-pkg, because you can have multiple versions of the same package installed.
It's as if every version is an entirely different package, with how that in many respects the version becomes a part of the package name (e.g. mustaches-0.1.0.0) -- and maybe it really is for ghc-pkg (I'm not entirely familiar with it, but it would make sense).

解决方案

You have scenarios like this:

Where both B and C depend on A. However, if they were installed at different times, they may depend on different versions of A. For example, A version 1 export type T = Int, but in version 2 it exports type T = Bool.

Only when you try to build D do you expose the problem that B and C were build against different versions of A, and you can't compare T version 1 against T version 2.

这篇关于cabal（依赖）地狱背后的原因是什么？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！