为什么我不能导入这个Haskell模块？ [英] Why can't I import this Haskell module?

问题描述

我把它放在〜/ Desktop / Shapes.hs 中：

 模块形状
（Shape（Rectangle）
）其中
 
 data Shape = Circle |矩形派生（显示）
  

然后我做到这一点：

  cd〜/桌面
 ghci 
 
 ghci> ：m +形状
 
 <无位置信息>：
找不到模块`形状'
它不是当前程序或任何已知包中的模块。 
 
 ghci>导入形状
 
 <无位置信息>：
找不到模块`形状'
它不是当前程序或任何已知软件包中的模块。 
  

为什么我得到这个错误？

我也试着先用 ghc -c Shapes.hs 编译。它仍然不起作用。

我在OS X 10.9.2上安装了来自haskell.org的Haskell Platform 2013.2.0.0 for Mac OS X，64位小牛。我也跟着他们的 ghc-clang-wrapper 指示。

更新

有人建议先做：l Shapes.hs 。问题是：l Shapes.hs 加载了整个Shapes文件，这意味着我可以访问 Circle code>值构造函数，即使我没有导出它。查看我之前的问题：为什么我可以使用这个私人值构造函数？我只想加载模块。这可能吗？

解决方案

您需要加载 Shapes.hs 首先由：l Shapes.hs 。

1. 因为您的 Shapes 尚未加载，因此：m Shapes 不起作用。


因为你的 Shapes 不存在于 ghci 可以找到的编译包中，所以 import Shapes 不起作用。 在：load 模块之后，可以使用：module 或 import 只能导入这些符号。例如，在之后：load Shapes.hs 和：module Shapes ， Rectangle


请参阅：

href =http://www.haskell.org/ghc/docs/latest/html/users_guide/interactive-evaluation.html#ghci-scope =nofollow>提示符的范围有多大？

：module和：加载




I put this in ~/Desktop/Shapes.hs:

module Shapes   
( Shape(Rectangle)
) where 

data Shape = Circle | Rectangle deriving (Show)

I then do this:

cd ~/Desktop
ghci

ghci> :m +Shapes

<no location info>:
    Could not find module `Shapes'
    It is not a module in the current program, or in any known package.

ghci> import Shapes

<no location info>:
    Could not find module `Shapes'
    It is not a module in the current program, or in any known package.

Why do I get this error?

I also tried compiling first with ghc -c Shapes.hs. It still doesn't work.

I installed the "Haskell Platform 2013.2.0.0 for Mac OS X, 64 bit" from haskell.org on my OS X 10.9.2 Mavericks. I also followed their ghc-clang-wrapper instructions.

Update:

Someone suggested doing :l Shapes.hs first. The problem is that :l Shapes.hs loads the entire Shapes file, meaning I have access to the Circle value constructor even if I did not export it. See my earlier question: Why can I use this "private" value constructor? I want to load only the module. Is this possible?

解决方案

You need to load your Shapes.hs first by :l Shapes.hs.

1. Because your Shapes have not been loaded, so :m Shapes will not work.

2. Because your Shapes does not exist in a compiled package that ghci can find, so import Shapes will not work.

If you only want the exported symbols in scope, after :load a module, you could use :module or import to only import those symbols. For example, after :load Shapes.hs and :module Shapes, Rectangle will in scope but Circle will not.

See:
What's really in scope at the prompt?
:module and :load

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