如何用库+可执行文件构建一个Haskell cabal项目，该项目仍然可以通过runhaskell / ghci运行？ [英] How to make a Haskell cabal project with library+executables that still run with runhaskell/ghci?

问题描述

如果您在cabal中声明库+可执行部分文件，同时避免库的双重编译，将库放入 hs-source-dirs 目录中，通常不能使用 ghci 和 runhaskell ，特别是如果可执行文件本身有辅助模块的话。

什么是推荐的项目布局

• 只会构建一次所需的内容


• 允许使用 runhaskell


• 有干净的结构，没有黑客？ h2_lin>解决方案

假设您有一个 mylib 库，并且 mylib-commandline 和 mylib-server 可执行文件。

您可以使用 hs-source-dirs 用于库和每个可执行文件，以便每个文件都有自己的项目根目录，避免双重编译：



  mylib /＃项目根目录
 mylib.cabal 
 src /＃根目录该库
 tests / 
 mylib-commandline /＃命令行实用程序的辅助工具+辅助程序模块
 mylib-server /＃Web服务+辅助程序模块的根目录
  
 
 $ b 
完整的目录布局：
 
 
  mylib /＃项目根目录
 mylib.cabal 
 src /＃库的根目录
 Web / 
 Mylib.hs＃主库模块
 Mylib / 
 ModuleA＃Mylib.ModuleA 
 ModuleB＃Mylib.ModuleB 
 tests / 
 ... 
 mylib-commandline /＃命令行实用程序的根目录
 Main.hs＃ 模块主要在哪里存根main = Web.Mylib.Commandline.Main.main
 Web / 
 Mylib / 
命令行/ 
 Main.hs＃CLI入口点
 Arguments.hs＃程序命令行参数解析器
 mylib-server /＃Web服务的根目录
 Server.hs＃module Main stub withmain = Web.Mylib.Server.Main.main
 Web / 
 Mylib / 
服务器/ 
 Main.hs＃服务器入口点
参数.hs＃服务器命令行参数解析器
  
 入口点文件 mylib-commandline / Main.hs 看起来像这样： 
 
 
  module主要在
 
中导入限定的Web.Mylib.Server.Main作为MylibServer 
 
 main :: IO（）
 main = MylibServer.main 
  
您需要它们是因为可执行文件必须在一个简单的 Main 。
 
 
 
您的 mylib.cabal 看起来像这样：  
 
 
  library 
 hs-source-dirs：src 
 exposed-modules：
 Web.Mylib 
 Web.Mylib.ModuleA 
 Web.Mylib.ModuleB 
 build-depends： 
 base> = 4&& < = 5 
，[库的其他依赖关系] 
 
可执行mylib-commandline 
 hs-source-dirs：mylib-commandline 
 main-is：Main .hs 
 other-modules：
 Web.Mylib.Commandline.Main 
 Web.Mylib.Commandline.Arguments 
 build-depends：
ase> = 4& amp ;&安培; < = 5 
，mylib 
，[CLI的其他依赖性] 
 
可执行文件mylib-server 
 hs-source-dirs：mylib-server 
 main-is：Server.hs 
 other-modules：
 Web.Mylib.Server.Main 
 build-depends：
 base> = 4&& < = 5 
，mylib 
，warp> = XX 
，[服务器的其他依赖关系] 
  
 
 
 $  cabal build 将构建库和两个可执行文件，而不需要对库进行双重编译，因为每个文件都在它们自己的 hs-source-dirs 并且可执行文件依赖于库。
 
 
 
您仍然可以使用 runghc ，使用 -i 开关来告诉它应该在哪里寻找模块（使用：作为分隔符）：
  runhaskell -isrc：mylib-commandline mylib-commandline / Main.hs 
 
 runhaskell -isrc：mylib-server mylib-server / Server.hs 
  
方式，你可以有一个干净的布局，带有助手模块的可执行文件，并且所有东西都可以在 runhaskell  /  runghc 和 ghci中。为避免重复输入此标志，可以添加类似于 
 
 
 ：set -isrc：mylib-commandline：mylib-server 
  
添加到您的 .ghci 文件中。
 
 
 
 
 
 
请注意，有时应该将您的代码拆分为不同的包，例如 mylib ， mylib-commandline 和 mylib-server 。
 
If you declare a library + executable sections in a cabal file while avoiding double compilation of the library by putting the library into a hs-source-dirs directory, you cannot usually run your project with ghci and runhaskell anymore, especially if the executables have helper modules themselves.

What is a recommended project layout that


only builds what is needed once
allows using runhaskell
has a clean structure without hacks?

解决方案
Let's assume you have a mylib library, and mylib-commandline and mylib-server executables.

You use hs-source-dirs for the library and each executable so that each has their own project root, avoiding double compilation:
mylib/                      # Project root
  mylib.cabal
  src/                      # Root for the library
  tests/
  mylib-commandline/        # Root for the command line utility + helper modules
  mylib-server/             # Root for the web service + helper modules
Full directory layout:
mylib/                      # Project root
  mylib.cabal
  src/                      # Root for the library
    Web/
      Mylib.hs              # Main library module
      Mylib/
        ModuleA             # Mylib.ModuleA
        ModuleB             # Mylib.ModuleB
  tests/
    ...
  mylib-commandline/        # Root for the command line utility
    Main.hs                 # "module Main where" stub with "main = Web.Mylib.Commandline.Main.main"
    Web/
      Mylib/
        Commandline/
          Main.hs           # CLI entry point
          Arguments.hs      # Programm command line arguments parser
  mylib-server/             # Root for the web service
    Server.hs               # "module Main where" stub with "main = Web.Mylib.Server.Main.main"
    Web/
      Mylib/
        Server/
          Main.hs           # Server entry point
          Arguments.hs      # Server command line arguments parser
The stub-like entry point file mylib-commandline/Main.hs looks like this:
module Main where

import qualified Web.Mylib.Server.Main as MylibServer

main :: IO ()
main = MylibServer.main
You need them because an executable must start on a module simply called Main.

Your mylib.cabal looks like this:
library
  hs-source-dirs:   src
  exposed-modules:
    Web.Mylib
    Web.Mylib.ModuleA
    Web.Mylib.ModuleB
  build-depends:
      base >= 4 && <= 5
    , [other dependencies of the library]

executable mylib-commandline
  hs-source-dirs:   mylib-commandline
  main-is:          Main.hs
  other-modules:
    Web.Mylib.Commandline.Main
    Web.Mylib.Commandline.Arguments
  build-depends:
      base >= 4 && <= 5
    , mylib
    , [other depencencies for the CLI]

executable mylib-server
  hs-source-dirs:   mylib-server
  main-is:          Server.hs
  other-modules:
    Web.Mylib.Server.Main
  build-depends:
      base >= 4 && <= 5
    , mylib
    , warp >= X.X
    , [other dependencies for the server]
cabal build will build the library and the two executables without double compilation of the library, because each is in their own hs-source-dirs and the executables depend on the library.

You can still run the executables with runghc from your project root, using the -i switch to tell where it shall look for modules (using : as separator):
runhaskell -isrc:mylib-commandline mylib-commandline/Main.hs

runhaskell -isrc:mylib-server mylib-server/Server.hs
This way, you can have a clean layout, executables with helper modules, and everything still works with runhaskell/runghc and ghci. To avoid typing this flag repeatedly, you can add something similar to
:set -isrc:mylib-commandline:mylib-server
to your .ghci file.



Note that sometimes should split your code into separate packages, e.g. mylib, mylib-commandline and mylib-server.

                        
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