+-- ---------------------------------------------------------------------------
+-- User code exception handling
+
+-- This is the exception handler for exceptions generated by the
+-- user's code and exceptions coming from children sessions;
+-- it normally just prints out the exception. The
+-- handler must be recursive, in case showing the exception causes
+-- more exceptions to be raised.
+--
+-- Bugfix: if the user closed stdout or stderr, the flushing will fail,
+-- raising another exception. We therefore don't put the recursive
+-- handler arond the flushing operation, so if stderr is closed
+-- GHCi will just die gracefully rather than going into an infinite loop.
+handler :: Exception -> GHCi Bool
+handler (DynException dyn)
+ | Just StopChildSession <- fromDynamic dyn
+ -- propagate to the parent session
+ = do ASSERTM (liftM not isTopLevel)
+ throwDyn StopChildSession
+
+ | Just StopParentSession <- fromDynamic dyn
+ = do at_topLevel <- isTopLevel
+ if at_topLevel then return True else throwDyn StopParentSession
+
+ | Just (ChildSessionStopped msg) <- fromDynamic dyn
+ = io(putStrLn msg) >> return False
+
+handler exception = do
+ flushInterpBuffers
+ io installSignalHandlers
+ ghciHandle handler (showException exception >> return False)
+
+showException (DynException dyn) =
+ case fromDynamic dyn of
+ Nothing -> io (putStrLn ("*** Exception: (unknown)"))
+ Just Interrupted -> io (putStrLn "Interrupted.")
+ Just (CmdLineError s) -> io (putStrLn s) -- omit the location for CmdLineError
+ Just ph@PhaseFailed{} -> io (putStrLn (showGhcException ph "")) -- ditto
+ Just other_ghc_ex -> io (print other_ghc_ex)
+
+showException other_exception
+ = io (putStrLn ("*** Exception: " ++ show other_exception))
+
+-----------------------------------------------------------------------------
+-- recursive exception handlers
+
+-- Don't forget to unblock async exceptions in the handler, or if we're
+-- in an exception loop (eg. let a = error a in a) the ^C exception
+-- may never be delivered. Thanks to Marcin for pointing out the bug.
+
+ghciHandle :: (Exception -> GHCi a) -> GHCi a -> GHCi a
+ghciHandle h (GHCi m) = GHCi $ \s ->
+ Exception.catch (m s)
+ (\e -> unGHCi (ghciUnblock (h e)) s)
+
+ghciUnblock :: GHCi a -> GHCi a
+ghciUnblock (GHCi a) = GHCi $ \s -> Exception.unblock (a s)
+
+
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