X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Control%2FException.hs;h=5362610db47b7241ceddc38339d9b4e3350e724b;hb=0a41af38169035a4359c0c29bc1219af564dce64;hp=aed144b55335948113d9cbe5eb921ddfe8e3c6c7;hpb=19de173b1bd4fa8cf1854cfefa619565910137f3;p=ghc-base.git

diff --git a/Control/Exception.hs b/Control/Exception.hs
index aed144b..5362610 100644
--- a/Control/Exception.hs
+++ b/Control/Exception.hs
@@ -103,6 +103,7 @@ module Control.Exception (
 
 	bracket,  	-- :: IO a -> (a -> IO b) -> (a -> IO c) -> IO ()
 	bracket_, 	-- :: IO a -> IO b -> IO c -> IO ()
+	bracketOnError,
 
 	finally, 	-- :: IO a -> IO b -> IO a
 	
@@ -117,7 +118,7 @@ import GHC.Base		( assert )
 import GHC.Exception 	as ExceptionBase hiding (catch)
 import GHC.Conc		( throwTo, ThreadId )
 import Data.IORef	( IORef, newIORef, readIORef, writeIORef )
-import Foreign.C.String ( CString, withCStringLen )
+import Foreign.C.String ( CString, withCString )
 import System.IO	( stdout, hFlush )
 #endif
 
@@ -130,13 +131,6 @@ import System.IO.Error	hiding ( catch, try )
 import System.IO.Unsafe (unsafePerformIO)
 import Data.Dynamic
 
-#include "Typeable.h"
-INSTANCE_TYPEABLE0(Exception,exceptionTc,"Exception")
-INSTANCE_TYPEABLE0(IOException,ioExceptionTc,"IOException")
-INSTANCE_TYPEABLE0(ArithException,arithExceptionTc,"ArithException")
-INSTANCE_TYPEABLE0(ArrayException,arrayExceptionTc,"ArrayException")
-INSTANCE_TYPEABLE0(AsyncException,asyncExceptionTc,"AsyncException")
-
 -----------------------------------------------------------------------------
 -- Catching exceptions
 
@@ -169,13 +163,12 @@ INSTANCE_TYPEABLE0(AsyncException,asyncExceptionTc,"AsyncException")
 -- might be a 'ThreadKilled', for example).  In this case it is usually better
 -- to use 'catchJust' and select the kinds of exceptions to catch.
 --
--- Also note that The "Prelude" also exports a
--- function called 'catch' which has the same type as
--- 'Control.Exception.catch', the difference being that the
--- "Prelude" version only catches the IO and user
+-- Also note that the "Prelude" also exports a function called
+-- 'Prelude.catch' with a similar type to 'Control.Exception.catch',
+-- except that the "Prelude" version only catches the IO and user
 -- families of exceptions (as required by Haskell 98).  We recommend
 -- either hiding the "Prelude" version of
--- 'catch' when importing
+-- 'Prelude.catch' when importing
 -- "Control.Exception", or importing
 -- "Control.Exception" qualified, to avoid name-clashes.
 
@@ -235,7 +228,7 @@ mapException f v = unsafePerformIO (catch (evaluate v)
 -- 'try' and variations.
 
 -- | Similar to 'catch', but returns an 'Either' result which is
--- @(Right a)@ if no exception was raised, or @(Left e)@ if an
+-- @('Right' a)@ if no exception was raised, or @('Left' e)@ if an
 -- exception was raised and its value is @e@.
 --
 -- >  try a = catch (Right \`liftM\` a) (return . Left)
@@ -244,6 +237,11 @@ mapException f v = unsafePerformIO (catch (evaluate v)
 -- to re-throw the exception after performing whatever cleanup is needed.
 -- Otherwise, 'tryJust' is generally considered to be better.
 --
+-- Also note that "System.IO.Error" also exports a function called
+-- 'System.IO.Error.try' with a similar type to 'Control.Exception.try',
+-- except that it catches only the IO and user families of exceptions
+-- (as required by the Haskell 98 @IO@ module).
+
 try :: IO a -> IO (Either Exception a)
 try a = catch (a >>= \ v -> return (Right v)) (\e -> return (Left e))
 
@@ -393,6 +391,21 @@ a `finally` sequel =
 bracket_ :: IO a -> IO b -> IO c -> IO c
 bracket_ before after thing = bracket before (const after) (const thing)
 
+-- | Like bracket, but only performs the final action if there was an 
+-- exception raised by the in-between computation.
+bracketOnError
+	:: IO a		-- ^ computation to run first (\"acquire resource\")
+	-> (a -> IO b)  -- ^ computation to run last (\"release resource\")
+	-> (a -> IO c)	-- ^ computation to run in-between
+	-> IO c		-- returns the value from the in-between computation
+bracketOnError before after thing =
+  block (do
+    a <- before 
+    catch 
+	(unblock (thing a))
+	(\e -> do { after a; throw e })
+ )
+
 -- -----------------------------------------------------------------------------
 -- Asynchronous exceptions
 
@@ -470,23 +483,6 @@ Similar arguments apply for other interruptible operations like
 'System.IO.openFile'.
 -}
 
--- -----------------------------------------------------------------------------
--- Assert
-
-#ifdef __HADDOCK__
--- | If the first argument evaluates to 'True', then the result is the
--- second argument.  Otherwise an 'AssertionFailed' exception is raised,
--- containing a 'String' with the source file and line number of the
--- call to assert.
---
--- Assertions can normally be turned on or off with a compiler flag
--- (for GHC, assertions are normally on unless the @-fignore-asserts@
--- option is give).  When assertions are turned off, the first
--- argument to 'assert' is ignored, and the second argument is
--- returned as the result.
-assert :: Bool -> a -> a
-#endif
-
 #ifndef __GLASGOW_HASKELL__
 assert :: Bool -> a -> a
 assert True x = x
@@ -506,10 +502,11 @@ uncaughtExceptionHandler = unsafePerformIO (newIORef defaultHandler)
                Deadlock    -> "no threads to run:  infinite loop or deadlock?"
                ErrorCall s -> s
                other       -> showsPrec 0 other "\n"
-         withCStringLen ("Fail: "++msg) $ \(cstr,len) -> writeErrString cstr len
-         
-foreign import ccall unsafe "writeErrString__"
-	writeErrString :: CString -> Int -> IO ()
+         withCString "%s" $ \cfmt ->
+          withCString msg $ \cmsg ->
+            errorBelch cfmt cmsg
+
+foreign import ccall unsafe errorBelch :: CString -> CString -> IO ()
 
 setUncaughtExceptionHandler :: (Exception -> IO ()) -> IO ()
 setUncaughtExceptionHandler = writeIORef uncaughtExceptionHandler