如何从父目录导入Haskell模块？附具体目录结构场景

Hey there! Let's tackle this Haskell module import issue with your directory structure. First, let's recap your setup to make sure I'm on the same page:

root
├── scripts
│   └── script1.hs
└── source
    ├── librarymodule.hs
    └── libraryconfig.txt

You need script1.hs to use functions from librarymodule.hs, which also relies on libraryconfig.txt in the same source directory. Here are a few solid solutions depending on whether you want a quick fix or a more maintainable setup:

Quick Fix: Use GHC's -i Flag #

This is the simplest way to get things running without restructuring your project:

• First, fix a common Haskell gotcha: module names must match filenames (case-sensitive). Rename librarymodule.hs to LibraryModule.hs so you can properly import it as import LibraryModule in script1.hs.
• To handle the config file path reliably: Don't use a relative path like "./libraryconfig.txt" in LibraryModule.hs (since your working directory might be root or scripts when running the script). Instead, use a path relative to your project root:

  import System.FilePath ((</>))
  import System.Directory (getCurrentDirectory)
  
  getConfigPath :: IO FilePath
  getConfigPath = do
      projectRoot <- getCurrentDirectory
      return $ projectRoot </> "source" </> "libraryconfig.txt"
  

• Compile or run script1.hs from the root directory with the -i flag to tell GHC where to find the source module:

  # Compile to an executable
  ghc -isource scripts/script1.hs
  # Or run directly without compiling
  runhaskell -isource scripts/script1.hs
  

Maintainable Setup: Cabal Project #

If you plan to expand this project, using Cabal (Haskell's official build tool) will make dependency and resource management easier:

1. Create a myproject.cabal file in your root directory with this content:

   cabal-version: 3.0
   name: myproject
   version: 0.1.0.0
   
   executable script1
       main-is: script1.hs
       hs-source-dirs: scripts, source
       build-depends: base >=4.14 && <5
       default-language: Haskell2010
       data-files: source/libraryconfig.txt
   

2. Update LibraryModule.hs to use Cabal's auto-generated path module to find the config file (this works even if you install the project later):

   import Paths_myproject (getDataFileName)
   
   getConfigPath :: IO FilePath
   getConfigPath = getDataFileName "source/libraryconfig.txt"
   

3. Run your script with:

   cabal run script1
   

Alternative: Stack Project #

If you prefer using Stack (a popular Haskell toolchain manager), follow these steps:

1. Run stack init in your root directory to generate a package.yaml and stack.yaml.
2. Edit package.yaml to include your source directories and config file:

   name: myproject
   version: 0.1.0.0
   
   executables:
     script1:
       main: script1.hs
       source-dirs: scripts, source
       ghc-options:
         - -threaded
         - -rtsopts
         - -with-rtsopts=-N
       dependencies:
         - base >=4.14 && <5
       data-files: source/libraryconfig.txt
   

3. Use the same Paths_myproject approach in LibraryModule.hs as the Cabal solution to fetch the config path.
4. Run your script with:

   stack run script1
   

内容的提问来源于stack exchange，提问作者JonasAnon