Fw: Re: Re[2]: No more ExitException? <- documentation bug

Volker Wysk vw at volker-wysk.de
Thu Jan 28 02:32:57 EST 2010

The following message went to Bulat Ziganshin alone. So here it is for the mailing list. Sorry.

Begin forwarded message:

On Wed, 27 Jan 2010 12:43:13 +0300
Bulat Ziganshin <bulat.ziganshin at gmail.com> wrote:

> > exitWith throws the ExitCode when it is called. This leads to the
> > shutdown of the program, if it isn't caught. Just like ExitException.
> > This isn't documented.
> i've googled for "exitWith throws the ExitCode" and it pointed me to
> the exitWith docs: "Computation exitWith code throws ExitException code."

This is the source code of exitWith:


-- ---------------------------------------------------------------------------
-- exitWith

-- | Computation 'exitWith' @code@ throws 'ExitException' @code at .
-- Normally this terminates the program, returning @code@ to the
-- program's caller.  Before the program terminates, any open or
-- semi-closed handles are first closed.
-- A program that fails in any other way is treated as if it had
-- called 'exitFailure'.
-- A program that terminates successfully without calling 'exitWith'
-- explicitly is treated as it it had called 'exitWith' 'ExitSuccess'.
-- As an 'ExitException' is not an 'IOError', 'exitWith' bypasses
-- the error handling in the 'IO' monad and cannot be intercepted by
-- 'catch' from the "Prelude".  However it is an 'Exception', and can
-- be caught using the functions of "Control.Exception".  This means
-- that cleanup computations added with 'Control.Exception.bracket'
-- (from "Control.Exception") are also executed properly on 'exitWith'.

#ifndef __NHC__
exitWith :: ExitCode -> IO a
exitWith ExitSuccess = throwIO ExitSuccess
exitWith code@(ExitFailure n)
  | n /= 0 = throwIO code
  | otherwise = ioError (IOError Nothing InvalidArgument "exitWith" "ExitFailure 0" Nothing)
#endif  /* ! __NHC__ */


As you can see, it throws the ExitCode, not an ExitException. The documentation is faulty.


Volker Wysk <vw at volker-wysk.de>

Volker Wysk <vw at volker-wysk.de>

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