1 files changed, 35 insertions, 0 deletions

diff --git a/src/Data/JLD/Control/Monad/RES.hs b/src/Data/JLD/Control/Monad/RES.hs
new file mode 100644
index 0000000..1c96d46
--- /dev/null
+++ b/src/Data/JLD/Control/Monad/RES.hs
@@ -0,0 +1,35 @@
+module Data.JLD.Control.Monad.RES (
+    REST,
+    runREST,
+    evalREST,
+    withEnvRES,
+    withErrorRES,
+    withErrorRES',
+    withStateRES,
+) where
+
+import Data.JLD.Prelude
+
+import Control.Monad.Except (mapExceptT)
+
+type REST r e s m = ReaderT r (ExceptT e (StateT s m))
+
+runREST :: r -> s -> REST r e s m a -> m (Either e a, s)
+runREST env st = flip runReaderT env .> runExceptT .> flip runStateT st
+
+evalREST :: Monad m => r -> s -> REST r e s m a -> m (Either e a)
+evalREST env st = flip runReaderT env .> runExceptT .> flip evalStateT st
+
+withEnvRES :: (r -> r') -> REST r' e s m a -> REST r e s m a
+withEnvRES fn (ReaderT m) = ReaderT <| fn .> m
+
+withErrorRES :: Functor m => (e' -> e) -> REST r e' s m a -> REST r e s m a
+withErrorRES fn (ReaderT m) = ReaderT <| m .> mapExceptT (fmap <| first fn)
+
+withErrorRES' :: Monad m => (e' -> REST r e s m a) -> REST r e' s m a -> REST r e s m a
+withErrorRES' fn (ReaderT m) =
+    ReaderT <| \r -> m r |> mapExceptT \m' -> m' >>= either (fn .> flip runReaderT r .> runExceptT) (Right .> pure)
+
+withStateRES :: Monad m => (s -> s') -> (s -> s' -> s) -> REST r e s' m a -> REST r e s m a
+withStateRES fin fout (ReaderT m) =
+    ReaderT \env -> m env |> mapExceptT \st -> StateT \s -> second (fout s) <$> runStateT st (fin s)