Haskell - exit a program with a specified error code

Question

In Haskell, is there a way to exit a program with a specified error code? The resources I've been reading typically point to the error function for exiting a program with an error, but it seems to always terminate the program with an error code of 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

Use exitWith from System.Exit:

main = exitWith (ExitFailure 2)

I would add some helpers for convenience:

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

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

Answer 2

An alternative that allows an error message only is 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)

The accepted answer allows setting the exit error code though, so it's closer to the exact phrasing of the question.