[Haskell-beginners] Proper use of exit{Success,Failure}

[Sumit Sahrawat, Maths & Computing, IIT (BHU)]

Try `Control.Monad.void`. It is equivalent of adding `>> return ()` to the
end of a block.

void $ do
 ...

On 9 June 2015 at 20:55, Vale Cofer-Shabica <vale.cofershabica at gmail.com>
wrote:

> Dear all,
>
> I'm writing a command line program which may need to exit early based
> on some condition. Because of the pipeline the program is a part of, I
> want to be able to control the exit status when it does terminate. I
> can successfully use 'error' to indicate failure, but also want to
> exit early with success (or any other status). Here's what I've
> managed:
>
> >import System.Exit (exitSuccess)
> >import Control.Monad (when)
>
> >main = do
>
> ... code to reasonably initialize condition, e.g.:
>
> >  let condition = True
> >  when condition (putStrLn "Bailing out.")>>exitSuccess>>(return ())
>
> ... program continues
>
> If I remove ">>(return ())" my code will not typecheck because
> "exitSuccess :: IO a". But this looks ugly and smells sufficiently
> like a kludge that I presume there is a better way to do it.
>
> Any suggestions appreciated,
> vale
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-- 
Regards

Sumit Sahrawat
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