[project @ 2000-03-13 10:53:55 by simonmar]

[ghc-hetmet.git] / ghc / lib / std / PrelException.lhs

diff --git a/ghc/lib/std/PrelException.lhs b/ghc/lib/std/PrelException.lhs
index d434c5a..0a548df 100644 (file)
--- a/ghc/lib/std/PrelException.lhs
+++ b/ghc/lib/std/PrelException.lhs
@@ -1,5 +1,5 @@
 % -----------------------------------------------------------------------------
-% $Id: PrelException.lhs,v 1.9 1999/11/11 15:18:00 simonmar Exp $
+% $Id: PrelException.lhs,v 1.11 2000/01/30 10:25:28 simonmar Exp $
 %
 % (c) The GRAP/AQUA Project, Glasgow University, 1998
 %
@@ -38,7 +38,6 @@ data Exception
   | AssertionFailed    String          -- Assertions
   | DynException       Dynamic         -- Dynamic exceptions
   | AsyncException     AsyncException  -- Externally generated errors
-  | ArrayException     ArrayException  -- Array-related exceptions
   | NonTermination
 
 data ArithException
@@ -55,11 +54,6 @@ data AsyncException
   | ThreadKilled
   deriving (Eq, Ord)
 
-data ArrayException
-  = IndexOutOfBounds String
-  | UndefinedElement String
-  deriving (Eq, Ord)
-
 stackOverflow, heapOverflow :: Exception -- for the RTS
 stackOverflow = AsyncException StackOverflow
 heapOverflow  = AsyncException HeapOverflow
@@ -76,12 +70,6 @@ instance Show AsyncException where
   showsPrec _ HeapOverflow    = showString "heap overflow"
   showsPrec _ ThreadKilled    = showString "thread killed"
 
-instance Show ArrayException where
-  showsPrec _ (IndexOutOfBounds s) = showString "array index out of bounds: "
-                                  . showString s
-  showsPrec _ (UndefinedElement s) = showString "undefined array element: "
-                                  . showString s
-
 instance Show Exception where
   showsPrec _ (IOException err)                 = shows err
   showsPrec _ (ArithException err)       = shows err
@@ -108,22 +96,24 @@ throw exception = raise# exception
 #endif
 \end{code}
 
-catch handles the passing around of the state in the IO monad; if we
-don't actually apply (and hence run) an IO computation, we don't get
-any exceptions!  Hence a large mantrap to watch out for is
+catchException used to handle the passing around of the state to the
+action and the handler.  This turned out to be a bad idea - it meant
+that we had to wrap both arguments in thunks so they could be entered
+as normal (remember IO returns an unboxed pair...).
+
+Now catch# has type
 
-       catch# (m :: IO ()) (handler :: NDSet Exception -> IO ())
+    catch# :: IO a -> (b -> IO a) -> IO a
 
-since the computation 'm' won't actually be performed in the context
-of the 'catch#'.  In fact, don't use catch# at all.
+(well almost; the compiler doesn't know about the IO newtype so we
+have to work around that in the definition of catchException below).
 
 \begin{code}
 catchException :: IO a -> (Exception -> IO a) -> IO a
 #ifdef __HUGS__
 catchException m k =  ST (\s -> unST m s `primCatch'` \ err -> unST (k err) s)
 #else
-catchException m k =  IO $ \s -> case catch# (liftIO m s) (\exs -> liftIO (k exs) s)
-                         of STret s1 r -> (# s1, r #)
+catchException (IO m) k =  IO $ \s -> catch# m (\ex -> unIO (k ex)) s
 #endif
 
 catch           :: IO a -> (IOError -> IO a) -> IO a