cabal（依赖）地狱背后的原因是什么？

问题描述

在Cabal-install中如何发生依赖关系？

我在：

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:

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.

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