Haskell - 退出带有指定错误代码的程序

Question

在Haskell中,有没有办法退出带有指定错误代码的程序？我一直在阅读的资源通常指向error退出程序时出错的函数,但似乎总是以错误代码终止程序1.

[martin@localhost Haskell]$ cat error.hs
main = do
    error "My English language error message"
[martin@localhost Haskell]$ ghc error.hs
[1 of 1] Compiling Main             ( error.hs, error.o )
Linking error ...
[martin@localhost Haskell]$ ./error 
error: My English language error message
[martin@localhost Haskell]$ echo $?
1

Answer 1

使用exitWith来自System.Exit:

main = exitWith (ExitFailure 2)

为方便起见,我会添加一些助手:

exitWithErrorMessage :: String -> ExitCode -> IO a
exitWithErrorMessage str e = hPutStrLn stderr str >> exitWith e

exitResourceMissing :: IO a
exitResourceMissing = exitWithErrorMessage "Resource missing" (ExitFailure 2)

Answer 2

仅允许错误消息的替代方法是die

import System.Exit

tests = ... -- some value from the program
testsResult = ... -- Bool value overall status

main :: IO ()
main = do
    if testsResult then
        print "Tests passed"
    else
        die (show tests)

不过，接受的答案允许设置退出错误代码，因此它更接近问题的确切措辞。