驚天動地預處理符號

Question

可能重複：
Haskell: Correct practice to specify version in source?

它是沒有辦法的陰謀元數據導出到我的代碼？使用自動工具，我定義了例如configure.ac中的程序版本，並將其作爲我的代碼的定義。在cabal中，目前，我必須在兩個地方保存程序版本 - 在.cabal和--version。優雅的解決方案

Answer 1

讓我用shell會話回答這個問題：

~ $ cd /tmp/ 
/tmp $ mkdir test 
/tmp $ cd test/ 
/tmp/test $ cabal init 
Package name? [default: test] 
Package version? [default: 0.1.0.0] 
Please choose a license: 
* 1) (none) 
    2) GPL-2 
    3) GPL-3 
    4) LGPL-2.1 
    5) LGPL-3 
    6) BSD3 
    7) MIT 
    8) PublicDomain 
    9) AllRightsReserved 
    10) Other (specify) 
Your choice? [default: (none)] 
Author name? [default: Joachim Breitner] 
Maintainer email? [default: mail@joachim-breitner.de] 
Project homepage URL? 
Project synopsis? 
Project category: 
* 1) (none) 
    2) Codec 
    3) Concurrency 
    4) Control 
    5) Data 
    6) Database 
    7) Development 
    8) Distribution 
    9) Game 
    10) Graphics 
    11) Language 
    12) Math 
    13) Network 
    14) Sound 
    15) System 
    16) Testing 
    17) Text 
    18) Web 
    19) Other (specify) 
Your choice? [default: (none)] 
What does the package build: 
    1) Library 
    2) Executable 
Your choice? 2 
Include documentation on what each field means (y/n)? [default: n] 

Guessing dependencies... 

Generating LICENSE... 
Warning: unknown license type, you must put a copy in LICENSE yourself. 
Generating Setup.hs... 
Generating test.cabal... 

Warning: no synopsis given. You should edit the .cabal file and add one. 
You may want to edit the .cabal file and add a Description field. 
/tmp/test $ vim *.cabal 
/tmp/test $ cat *.cabal 
name:    test 
version:    0.1.0.0 
license-file:  LICENSE 
author:    Joachim Breitner 
maintainer:   mail@joachim-breitner.de 
build-type:   Simple 
cabal-version:  >=1.8 

executable test 
    main-is: Main.hs 
    build-depends:  base ==4.5.* 

/tmp/test $ echo 'main = return()' > Main.hs 
/tmp/test $ cabal configure && cabal build 
Resolving dependencies... 
Configuring test-0.1.0.0... 
Warning: The 'license-file' field refers to the file 'LICENSE' which does not 
exist. 
Building test-0.1.0.0... 
Preprocessing executable 'test' for test-0.1.0.0... 
[1 of 1] Compiling Main    (Main.hs, dist/build/test/test-tmp/Main.o) 
Linking dist/build/test/test ... 
/tmp/test $ find dist/ 
dist/ 
dist/package.conf.inplace 
dist/setup-config 
dist/build 
dist/build/autogen 
dist/build/autogen/Paths_test.hs 
dist/build/autogen/cabal_macros.h 
dist/build/test 
dist/build/test/test-tmp 
dist/build/test/test-tmp/Main.o 
dist/build/test/test-tmp/Main.hi 
dist/build/test/test 
/tmp/test $ grep -i version dist/build/autogen/Paths_test.hs 
    version, 
import Data.Version (Version(..)) 
version :: Version 
version = Version {versionBranch = [0,1,0,0], versionTags = []} 
/tmp/test $ echo 'import Paths_test' > Main.hs 
/tmp/test $ echo 'main = print version' >> Main.hs 
/tmp/test $ cabal build 
Building test-0.1.0.0... 
Preprocessing executable 'test' for test-0.1.0.0... 
[1 of 2] Compiling Paths_test  (dist/build/autogen/Paths_test.hs, dist/build/test/test-tmp/Paths_test.o) 
[2 of 2] Compiling Main    (Main.hs, dist/build/test/test-tmp/Main.o) 
Linking dist/build/test/test ... 
/tmp/test $ ./dist/build/test/test 
Version {versionBranch = [0,1,0,0], versionTags = []} 

（TL; DR：陰謀生成一個名爲Paths_<pkgname>定義常量version :: Version模塊）