use mapLiftingReader for local

Co-authored-by: Ryan Hendrickson <[email protected]>
haskell · Apr 18, 2024 · 1843405 · 1843405
1 parent cad092e
commit 1843405
Showing 1 changed file with 5 additions and 2 deletions.
diff --git a/Control/Monad/Reader/Class.hs b/Control/Monad/Reader/Class.hs
@@ -213,10 +213,13 @@ newtype LiftingReader t m a = LiftingReader (t m a)
 
 instance MonadReader r m => MonadReader r (LiftingReader (ReaderT r') m) where
   ask = lift ask
-  local f (LiftingReader (ReaderT.ReaderT x)) = LiftingReader . ReaderT.ReaderT $ local f . x
+  local f = mapLiftingReader (ReaderT.mapReaderT (local f))
   reader = lift . reader
 
 instance (MonadReader r m, Monoid w) => MonadReader r (LiftingReader (LazyRWS.RWST r' w s) m) where
   ask = lift ask
-  local f (LiftingReader (LazyRWS.RWST x)) = LiftingReader . LazyRWS.RWST $ \r s -> local f $ x r s
+  local f = mapLiftingReader (LazyRWS.mapRWST (local f))
   reader = lift . reader
+
+mapLiftingReader :: (t m a -> t n b) -> LiftingReader t m a -> LiftingReader t n b
+mapLiftingReader = coerce