[project @ 2005-02-11 11:36:23 by simonmar]

[ghc-base.git] / Control / Exception.hs

diff --git a/Control/Exception.hs b/Control/Exception.hs
index 83f37cb..5362610 100644 (file)
--- 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
        
@@ -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
 
@@ -397,6 +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
 
@@ -474,23 +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