diff --git a/heftia-effects/Example/Continuation2/Main.hs b/heftia-effects/Example/Continuation2/Main.hs
index 8f73b03..20546a5 100644
--- a/heftia-effects/Example/Continuation2/Main.hs
+++ b/heftia-effects/Example/Continuation2/Main.hs
@@ -9,9 +9,17 @@ import Control.Effect.Interpreter.Heftia.ShiftReset (evalShift, runShift_)
 import Control.Effect.Interpreter.Heftia.State (evalState)
 import Control.Effect.Key (key)
 import Control.Monad.Extra (whenM)
-import Control.Monad.Hefty.Interpret (runEff)
-import Control.Monad.Hefty.Transform (unkey)
-import Control.Monad.Hefty.Types (Eff, send, sendN)
+import Control.Monad.Hefty (
+    Eff,
+    runEff,
+    send,
+    sendN,
+    unkey,
+    type (!!),
+    type ($),
+    type (+),
+    type (:+:),
+ )
 import Control.Monad.IO.Class (liftIO)
 import Data.Effect.Key (type (#>))
 import Data.Effect.Reader (Ask, Local, ask, local)
@@ -88,7 +96,7 @@ handleShiftThenReader = do
         & (evalState 0 . unkey)
         & runEff
   where
-    prog :: Eff '[Shift_, Local Int] '[Ask Int, "counter" #> State Int, IO] ()
+    prog :: Shift_ :+: Local Int !! Ask Int + "counter" #> State Int + IO $ ()
     prog = do
         k <- getCC_
         env <- ask @Int
diff --git a/heftia-effects/Example/Logging/Main.hs b/heftia-effects/Example/Logging/Main.hs
index a3fdd9e..53e37c7 100644
--- a/heftia-effects/Example/Logging/Main.hs
+++ b/heftia-effects/Example/Logging/Main.hs
@@ -13,6 +13,7 @@ import Control.Effect (type (<:), type (<<:), type (~>))
 import Control.Effect.Interpreter.Heftia.Reader (runReader)
 import Control.Effect.Interpreter.Heftia.State (evalState)
 import Control.Monad (when)
+import Control.Monad.Hefty (type (+))
 import Control.Monad.Hefty.Interpret (
     interposeRec,
     interposeRecH,
@@ -27,7 +28,7 @@ import Control.Monad.Hefty.Transform (
     raiseUnder,
     subsume,
  )
-import Control.Monad.Hefty.Types (Eff, Elab, type (:!!))
+import Control.Monad.Hefty.Types (Elab, type (!!), type (:!!))
 import Control.Monad.IO.Class (MonadIO, liftIO)
 import Data.Effect.OpenUnion.Internal.FO (type (<|))
 import Data.Effect.OpenUnion.Internal.HO (HFunctors, type (<<|))
@@ -187,7 +188,7 @@ limitThenSave =
         & saveLogChunk
         & runApp
 
-runApp :: Eff '[LogChunk] '[FileSystem, Time, Log, IO] ~> IO
+runApp :: LogChunk !! FileSystem + Time + Log + IO ~> IO
 runApp =
     runLogChunk
         >>> runDummyFS
diff --git a/heftia/heftia.cabal b/heftia/heftia.cabal
index 71789c3..30e4466 100644
--- a/heftia/heftia.cabal
+++ b/heftia/heftia.cabal
@@ -68,6 +68,7 @@ library
         Data.Effect.OpenUnion.Internal
         Data.Effect.OpenUnion.Internal.FO
         Data.Effect.OpenUnion.Internal.HO
+        Data.Effect.OpenUnion.Sum
 
     reexported-modules:
         Data.Effect,
diff --git a/heftia/src/Control/Monad/Hefty.hs b/heftia/src/Control/Monad/Hefty.hs
index 589611c..d420cdd 100644
--- a/heftia/src/Control/Monad/Hefty.hs
+++ b/heftia/src/Control/Monad/Hefty.hs
@@ -6,6 +6,7 @@ module Control.Monad.Hefty (
     module Control.Monad.Hefty.Interpret.State,
     module Control.Monad.Hefty.Transform,
     module Data.Effect.OpenUnion,
+    module Data.Effect.HFunctor,
 ) where
 
 import Control.Monad.Hefty.Interpret (
@@ -134,8 +135,10 @@ import Control.Monad.Hefty.Types (
     sendUnionBy,
     sendUnionH,
     sendUnionHBy,
+    type (!!),
     type ($),
     type ($$),
     type (:!!),
  )
+import Data.Effect.HFunctor (HFunctor, type (:+:))
 import Data.Effect.OpenUnion
diff --git a/heftia/src/Control/Monad/Hefty/Types.hs b/heftia/src/Control/Monad/Hefty/Types.hs
index c7ca09b..8925b6e 100644
--- a/heftia/src/Control/Monad/Hefty/Types.hs
+++ b/heftia/src/Control/Monad/Hefty/Types.hs
@@ -27,6 +27,7 @@ import Data.Effect.NonDet qualified as E
 import Data.Effect.OpenUnion.Internal (ElemAt)
 import Data.Effect.OpenUnion.Internal.FO (MemberBy, Union, inj, inj0, injN, type (<|))
 import Data.Effect.OpenUnion.Internal.HO (MemberHBy, UnionH, inj0H, injH, injNH, type (<<|))
+import Data.Effect.OpenUnion.Sum (SumToRecUnionList)
 import Data.Effect.Reader (Ask, Local, ask'', local'')
 import Data.Effect.State (State, get'', put'')
 import Data.Effect.Unlift (UnliftIO)
@@ -58,6 +59,9 @@ Allows writing @eh :!! ef@ instead of @Eff eh ef@.
 -}
 type (:!!) = Eff
 
+infixr 5 !!
+type eh !! ef = SumToRecUnionList UnionH eh :!! SumToRecUnionList Union ef
+
 instance Functor (Eff eh ef) where
     fmap f = \case
         Val x -> Val (f x)
diff --git a/heftia/src/Data/Effect/OpenUnion.hs b/heftia/src/Data/Effect/OpenUnion.hs
index c57b7aa..672e179 100644
--- a/heftia/src/Data/Effect/OpenUnion.hs
+++ b/heftia/src/Data/Effect/OpenUnion.hs
@@ -10,6 +10,7 @@ module Data.Effect.OpenUnion (
     module Data.Effect.OpenUnion.Internal,
     module Data.Effect.OpenUnion.Internal.HO,
     module Data.Effect.OpenUnion.Internal.FO,
+    module Data.Effect.OpenUnion.Sum,
 ) where
 
 import Data.Effect.OpenUnion.Internal (
@@ -121,5 +122,12 @@ import Data.Effect.OpenUnion.Internal.HO (
     (!!+.),
     type (<<|),
  )
+import Data.Effect.OpenUnion.Sum (
+    SumToRecUnion,
+    SumToRecUnionList,
+    U,
+    UL,
+    type (+),
+ )
 
--- TODO: add injN/prjN/move/swap/insert/rotate functions.
+-- TODO: add move/swap/insert/rotate functions.
diff --git a/heftia/src/Data/Effect/OpenUnion/Sum.hs b/heftia/src/Data/Effect/OpenUnion/Sum.hs
new file mode 100644
index 0000000..47e5a47
--- /dev/null
+++ b/heftia/src/Data/Effect/OpenUnion/Sum.hs
@@ -0,0 +1,26 @@
+-- SPDX-License-Identifier: MPL-2.0
+
+module Data.Effect.OpenUnion.Sum where
+
+import Data.Effect (LNop, Nop)
+import Data.Effect.HFunctor ((:+:))
+import Data.Effect.OpenUnion.Internal.FO (Union)
+import Data.Effect.OpenUnion.Internal.HO (UnionH)
+import GHC.Generics qualified as G
+
+infixr 5 +
+type (+) = (G.:+:)
+
+type U u e = SumToRecUnion u e
+type UL u e = SumToRecUnionList u e
+
+type SumToRecUnion u e = u (SumToRecUnionList u e)
+
+type SumToRecUnionList :: forall k. ([k] -> k) -> k -> [k]
+type family SumToRecUnionList u e where
+    SumToRecUnionList Union Nop = '[]
+    SumToRecUnionList Union (e + r) = e ': SumToRecUnionList Union r
+    SumToRecUnionList Union e = '[e]
+    SumToRecUnionList UnionH LNop = '[]
+    SumToRecUnionList UnionH (e :+: r) = e ': SumToRecUnionList UnionH r
+    SumToRecUnionList UnionH e = '[e]