\section[PrelMain]{Module @PrelMain@}
\begin{code}
+{-# OPTIONS -#include "cbits/stgio.h" #-}
+
module PrelMain( mainIO ) where
import Prelude
import {-# SOURCE #-} qualified Main -- for type of "Main.main"
-import PrelErr ( ioError )
+import IO ( hFlush, hPutStr, stdout, stderr )
+import PrelAddr ( Addr )
+import PrelException
+import PrelPack ( packString )
+import PrelArr ( ByteArray(..) )
\end{code}
\begin{code}
mainIO :: IO () -- It must be of type (IO t) because that's what
-- the RTS expects. GHC doesn't check this, so
-- make sure this type signature stays!
-mainIO = catch Main.main (\err -> ioError (showsPrec 0 err "\n"))
+mainIO = catchException Main.main handler
+
+-- make sure we handle errors while reporting the error!
+-- (e.g. evaluating the string passed to 'error' might generate
+-- another error, etc.)
+
+handler :: Exception -> IO ()
+handler err = catchException (real_handler err) handler
+
+real_handler :: Exception -> IO ()
+real_handler ex =
+ case ex of
+ ErrorCall s -> reportError s
+ other -> hPutStr stderr (showsPrec 0 other "\n") >>
+ _ccall_ stg_exit (1::Int)
+
+-- calls to 'error' are treated slightly differently...
+
+reportError :: String -> IO ()
+reportError str = do
+ (hFlush stdout) `catchException` (\ _ -> return ())
+ let bs@(ByteArray (_,len) _) = packString str
+ _ccall_ writeErrString__ (``&ErrorHdrHook''::Addr) bs len
+ _ccall_ stg_exit (1::Int)
+
\end{code}