New catchAsLeftM function

Author: newhoggy

src/Control/Monad/Oops.hs

@@ -32,6 +32,7 @@ module Control.Monad.Oops
     runOops,
     suspendM,
 
+    catchAsLeftM,
     catchAndExitFailureM,
 
     throwLeftM,
@@ -160,6 +161,14 @@ suspendM :: forall x m a n b. ()
   -> ExceptT x n b
 suspendM f = ExceptT . f . runExceptT
 
+-- | Catch the specified exception and return the caught value as 'Left'.  If no
+-- value was caught, then return the returned value in 'Right'.
+catchAsLeftM :: forall x e m a. ()
+  => Monad m
+  => ExceptT (Variant (x : e)) m a
+  -> ExceptT (Variant e) m (Either x a)
+catchAsLeftM = catchM @x (pure . Left) . fmap Right
+
 -- | Catch the specified exception.  If that exception is caught, exit the program.
 catchAndExitFailureM :: forall x e m a. ()
   => MonadIO m