+GHC's own exception type.
+
+\begin{code}
+ghcError :: GhcException -> a
+ghcError e = throwDyn e
+
+-- error messages all take the form
+--
+-- <location>: <error>
+--
+-- If the location is on the command line, or in GHC itself, then
+-- <location>="ghc". All of the error types below correspond to
+-- a <location> of "ghc", except for ProgramError (where the string is
+-- assumed to contain a location already, so we don't print one).
+
+data GhcException
+ = PhaseFailed String ExitCode -- an external phase (eg. cpp) failed
+ | Interrupted -- someone pressed ^C
+ | UsageError String -- prints the short usage msg after the error
+ | CmdLineError String -- cmdline prob, but doesn't print usage
+ | Panic String -- the `impossible' happened
+ | InstallationError String -- an installation problem
+ | ProgramError String -- error in the user's code, probably
+ deriving Eq
+
+progName = unsafePerformIO (getProgName)
+{-# NOINLINE progName #-}
+
+short_usage = "Usage: For basic information, try the `--help' option."
+
+instance Show GhcException where
+ showsPrec _ e@(ProgramError _) = showGhcException e
+ showsPrec _ e = showString progName . showString ": " . showGhcException e
+
+showGhcException (UsageError str)
+ = showString str . showChar '\n' . showString short_usage
+showGhcException (PhaseFailed phase code)
+ = showString phase . showString " failed, code = " . shows code
+showGhcException (CmdLineError str)
+ = showString str
+showGhcException (ProgramError str)
+ = showString str
+showGhcException (InstallationError str)
+ = showString str
+showGhcException (Interrupted)
+ = showString "interrupted"
+showGhcException (Panic s)
+ = showString ("panic! (the `impossible' happened, GHC version "
+ ++ cProjectVersion ++ "):\n\t"
+ ++ s ++ "\n\n"
+ ++ "Please report it as a compiler bug "
+ ++ "to glasgow-haskell-bugs@haskell.org,\n"
+ ++ "or http://sourceforge.net/projects/ghc/.\n\n")
+
+ghcExceptionTc = mkTyCon "GhcException"
+{-# NOINLINE ghcExceptionTc #-}
+instance Typeable GhcException where
+ typeOf _ = mkAppTy ghcExceptionTc []
+\end{code}
+
+Panics and asserts.
+