Question

我在（X）Ubuntu 15.10上使用Haskell版本7.8.4，而Cabal-Install 1.18都通过apt安装。我没有尝试在这台机器上手动安装任何与Haskell相关的东西。我设置了一个cabal沙箱，只提取并安装了一个模块，发现ghc似乎没有拿起它。 ghc -v似乎暗示我有两个版本的cabal库相互遮蔽。这是如何工作的？

我开始使用空目录/tmp/haskell-example

然后我做cabal sandbox init。

$ cabal sandbox init
Writing a default package environment file to
/tmp/haskell-example/cabal.sandbox.config
Creating a new sandbox at /tmp/haskell-example/.cabal-sandbox

然后我安装natural-numbers，因为我想在程序中使用Data.Natural模块。此操作成功。

$ cabal install natural-numbers
Resolving dependencies...
Notice: installing into a sandbox located at
/tmp/haskell-example/.cabal-sandbox
Configuring natural-numbers-0.1.2.0...
Building natural-numbers-0.1.2.0...
Installed natural-numbers-0.1.2.0

我可以验证Data.Natural模块确实已安装到cabal沙箱中。

$ ls /tmp/haskell-example/.cabal-sandbox/lib/x86_64-linux-ghc-7.8.4/natural-numbers-0.1.2.0
 Data
libHSnatural-numbers-0.1.2.0.a
libHSnatural-numbers-0.1.2.0-ghc7.8.4.so
$ ls /tmp/haskell-example/.cabal-sandbox/lib/x86_64-linux-ghc-7.8.4/natural-numbers-0.1.2.0/Data
Natural.dyn_hi
Natural.hi

然后我创建一个简单的Main.hs文件，导入Data.Natural但不使用它。

module Main where

import Data.Natural

main = putStrLn "Hello World"

当我尝试ghc Main.hs时，我会看到以下内容：

$ ghc Main.hs 
Main.hs:3:8:
    Could not find module ‘Data.Natural’
    Use -v to see a list of the files searched for.

启用详细标志后，似乎我的阴谋被后来的阴影所遮蔽了，后者又影响了早期的阴谋集团。为什么会这样？

$ ghc -v Main.hs 
Glasgow Haskell Compiler, Version 7.8.4, stage 2 booted by GHC version 7.8.4
Using binary package database: /usr/lib/ghc/package.conf.d/package.cache
hiding package Cabal-1.18.1.5 to avoid conflict with later version Cabal-1.22.1.1
wired-in package ghc-prim mapped to ghc-prim-0.3.1.0-ec14d2f6075975a2ce9112eae431c8e1
wired-in package integer-gmp mapped to integer-gmp-0.5.1.0-de4898ebdc5ab81cedce89121ae9ac84
wired-in package base mapped to base-4.7.0.2-5ef1e7e809bc3b18d74efc783356e209
wired-in package rts mapped to builtin_rts
wired-in package template-haskell mapped to template-haskell-2.9.0.0-c1976a420ad8b9b589eee08844c59ba2
wired-in package dph-seq not found.
wired-in package dph-par not found.
Hsc static flags: 
hiding package Cabal-1.18.1.5 to avoid conflict with later version Cabal-1.22.1.1
wired-in package ghc-prim mapped to ghc-prim-0.3.1.0-ec14d2f6075975a2ce9112eae431c8e1
wired-in package integer-gmp mapped to integer-gmp-0.5.1.0-de4898ebdc5ab81cedce89121ae9ac84
wired-in package base mapped to base-4.7.0.2-5ef1e7e809bc3b18d74efc783356e209
wired-in package rts mapped to builtin_rts
wired-in package template-haskell mapped to template-haskell-2.9.0.0-c1976a420ad8b9b589eee08844c59ba2
wired-in package dph-seq not found.
wired-in package dph-par not found.
*** Chasing dependencies:
Chasing modules from: *Main.hs

Main.hs:3:8:
    Could not find module ‘Data.Natural’
    Locations searched:
    Data/Natural.hs
    Data/Natural.lhs
*** Deleting temp files:
Deleting: 
*** Deleting temp dirs:
Deleting:

Answer 1

如果您正在进行手动黑客攻击，可以将沙箱的pkg db位置传递给ghc，例如：

ghc Main.hs -package-db .cabal-sandbox/x86_64-linux-ghc-7.10.2-packages.conf.d/

然而，使用沙箱的“正常”方式是始终使用cabal build（或cabal install没有参数）进行编译，而不是直接运行ghc。

运行cabal init，随意回答问题
修改生成的foo.cabal文件（foo是您的包名称。）
运行cabal build或cabal install - 这将为您运行ghc。

编辑cabal文件时，检查导出的模块（如果是lib）是否已列出，并且主src是否正确。还要确保natural-numbers子句中列出了build-depends:等依赖项。

GHC在cabal沙箱中找不到模块

1 个答案: