Add exception channel for asynchronous exceptions

Co-authored-by: Jan Beinke <git@janbeinke.com>

quasar.cabal

@@ -89,6 +89,7 @@ library
     Quasar.Async.Unmanaged
     Quasar.Awaitable
     Quasar.Disposable
+    Quasar.Exceptions
     Quasar.Observable
     Quasar.Observable.Delta
     Quasar.Observable.ObservableHashMap

src/Quasar/Exceptions.hs

+module Quasar.Exceptions (
+  ExceptionChannel(..),
+  throwToExceptionChannel,
+  catchInChannel,
+  catchAllInChannel,
+) where
+
+import Control.Concurrent.STM
+import Control.Monad.Catch
+import Quasar.Prelude
+
+
+newtype ExceptionChannel = ExceptionChannel (SomeException -> STM ())
+
+
+throwToExceptionChannel :: Exception e => ExceptionChannel -> e -> STM ()
+throwToExceptionChannel (ExceptionChannel channelFn) ex = channelFn (toException ex)
+
+-- TODO better name?
+catchInChannel :: forall e. Exception e => (e -> STM ()) -> ExceptionChannel -> ExceptionChannel
+catchInChannel handler parentChannel = ExceptionChannel $ mapM_ wrappedHandler . fromException
+  where
+    wrappedHandler :: e -> STM ()
+    wrappedHandler ex = catchAll (handler ex) (throwToExceptionChannel parentChannel)
+
+
+catchAllInChannel :: (SomeException -> STM ()) -> ExceptionChannel -> ExceptionChannel
+catchAllInChannel = catchInChannel