Add withException to Effectful.Exception (#311)

Author: arybczak

effectful-core/CHANGELOG.md

@@ -1,6 +1,7 @@
 # effectful-core-2.6.0.0 (????-??-??)
 * Adjust `generalBracket` with `base >= 4.21` to make use of the new exception
   annotation mechanism.
+* Add `withException` to `Effectful.Exception`.
 * **Breaking changes**:
   - Change the order of type parameters in `raise` for better usability.
   - `Effectful.Error.Static.ErrorWrapper` is no longer caught by `catchSync`.

effectful-core/src/Effectful/Exception.hs

@@ -59,6 +59,7 @@ module Effectful.Exception
   , C.ExitCase(..)
   , finally
   , onException
+  , withException
 
     -- * Utils
 
@@ -512,6 +513,27 @@ onException
 onException action handler = reallyUnsafeUnliftIO $ \unlift -> do
   E.onException (unlift action) (unlift handler)
 
+-- | A variant of 'onException' that gives access to the exception.
+--
+-- @since 2.6.0.0
+withException
+  :: E.Exception e
+  => Eff es a
+  -> (e -> Eff es b)
+  -- ^ Computation to run last when an exception or
+  -- t'Effectful.Error.Static.Error' was thrown.
+  -> Eff es a
+withException action cleanup = do
+#if MIN_VERSION_base(4,21,0)
+  action `catchNoPropagate` \ec@(E.ExceptionWithContext _ e) -> do
+    _ <- annotateIO (E.WhileHandling (E.toException ec)) (cleanup e)
+    rethrowIO ec
+#else
+  action `catch` \e -> do
+    _ <- cleanup e
+    throwIO e
+#endif
+
 ----------------------------------------
 -- Utils
 

effectful/CHANGELOG.md

@@ -1,6 +1,7 @@
 # effectful-core-2.6.0.0 (????-??-??)
 * Adjust `generalBracket` with `base >= 4.21` to make use of the new exception
   annotation mechanism.
+* Add `withException` to `Effectful.Exception`.
 * Re-export `ThreadId` from `Effectful.Concurrent` for convenience.
 * **Breaking changes**:
   - Change the order of type parameters in `raise` for better usability.