diff --git a/CHANGELOG.md b/CHANGELOG.md
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--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,11 @@
+# Changelog for `yaftee`
+
+All notable changes to this project will be documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
+and this project adheres to the
+[Haskell Package Versioning Policy](https://pvp.haskell.org/).
+
+## Unreleased
+
+## 0.1.0.0 - YYYY-MM-DD
diff --git a/LICENSE b/LICENSE
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--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,26 @@
+Copyright 2025 Yoshikuni Jujo
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+1.  Redistributions of source code must retain the above copyright notice, this
+    list of conditions and the following disclaimer.
+
+2.  Redistributions in binary form must reproduce the above copyright notice,
+    this list of conditions and the following disclaimer in the documentation
+    and/or other materials provided with the distribution.
+
+3.  Neither the name of the copyright holder nor the names of its contributors
+    may be used to endorse or promote products derived from this software
+    without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# try-yaftee
+
+see package yaftee-basic-monads and yaftee-conduit
diff --git a/Setup.hs b/Setup.hs
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--- /dev/null
+++ b/Setup.hs
@@ -0,0 +1,2 @@
+import Distribution.Simple
+main = defaultMain
diff --git a/src/Control/Monad/Yaftee/Eff.hs b/src/Control/Monad/Yaftee/Eff.hs
new file mode 100644
--- /dev/null
+++ b/src/Control/Monad/Yaftee/Eff.hs
@@ -0,0 +1,91 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE BlockArguments, LambdaCase #-}
+{-# LAnGUAGE RankNTypes #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# OPTIONS_GHC -Wall -fno-warn-tabs #-}
+
+module Control.Monad.Yaftee.Eff (
+
+	-- * TYPE
+
+	E,
+
+	-- * INJECTION
+
+	eff, effBase, effh,
+
+	-- * PROJECTION
+
+	run, runM, 
+
+	-- * HANDLE RELAY
+
+	handleRelay, handleRelayS, interpose
+
+	) where
+
+import Control.Monad.Fix
+import Control.Monad.HigherFreer qualified as HFreer
+import Control.HigherOpenUnion qualified as Union
+import Data.HigherFunctor qualified as HFunctor
+import Data.FTCQueue qualified as Q
+
+type E effs = HFreer.H (Union.U effs)
+
+eff :: Union.Member (Union.FromFirst t) effs => t a -> E effs i o a
+eff = (HFreer.:>>= Q.singleton HFreer.Pure) . Union.inj
+
+effBase :: Union.Base (Union.FromFirst t) effs => t a -> E effs i o a
+effBase = (HFreer.:>>= Q.singleton HFreer.Pure) . Union.injBase
+
+effh :: Union.Member h effs => h (E effs) i o a -> E effs i o a
+effh = (HFreer.:>>= Q.singleton HFreer.Pure) . Union.injh
+
+run :: E '[] i o a -> a
+run (HFreer.Pure x) = x
+run _ = error "bad"
+
+runM :: Monad m => E '[Union.FromFirst m] i o a -> m a
+runM (HFreer.Pure x) = pure x
+runM (u HFreer.:>>= q) = runM . (q HFreer.$) =<< Union.extract u
+
+handleRelay :: forall f t effs i o a .
+	HFunctor.Loose (Union.U effs) =>
+	(forall x . x -> f x) -> (forall x . f x -> x) ->
+	(forall x i' o' y . t x -> (x -> E effs i' o' (f y)) -> E effs i' o' (f y)) ->
+	E ((Union.FromFirst t) ': effs) i o a -> E effs i o (f a)
+handleRelay mk gx h = fix \go -> \case
+	HFreer.Pure x -> HFreer.Pure $ mk x
+	u HFreer.:>>= q -> case Union.decomp u of
+		Left u' -> HFunctor.map (handleRelay mk gx h) mk u' HFreer.:>>=
+			Q.singleton \x -> go $ q HFreer.$ gx x
+		Right (Union.FromFirst x k) -> h x ((go HFreer.. q) . k)
+
+handleRelayS :: forall f s t effs i o a .
+	HFunctor.Loose (Union.U effs) =>
+	(forall x . s -> x -> f s x) ->
+	(forall x . f s x -> s) -> (forall x . f s x -> x) ->
+	(forall x i' o' y .
+		t x -> (x -> s -> E effs i' o' y) -> s -> E effs i' o' y) ->
+	E ((Union.FromFirst t) ': effs) i o a -> s -> E effs i o (f s a)
+handleRelayS mk gs gx h m s0 = ($ m) . ($ s0) $ fix \go s -> \case
+	HFreer.Pure x -> HFreer.Pure $ mk s x
+	u HFreer.:>>= q -> case Union.decomp u of
+		Left u' -> HFunctor.map
+				(flip (handleRelayS mk gs gx h) s) (s `mk`) u'
+			HFreer.:>>= Q.singleton \xs ->
+				go (gs xs) $ q HFreer.$ gx xs
+		Right (Union.FromFirst x k) ->
+			h x (\x' s' -> (go s' HFreer.. q) . k $ x') s
+
+interpose :: forall eff effs i o a b .
+	Union.Member (Union.FromFirst eff) effs =>
+	(a -> E effs i o b) ->
+	(forall v . eff v -> (v -> E effs i o b) -> E effs i o b) -> E effs i o a -> E effs i o b
+interpose ret h = fix \go -> \case
+	HFreer.Pure x -> ret x
+	u HFreer.:>>= q -> case Union.prj u of
+		Just (Union.FromFirst x k) -> h x ((go HFreer.. q) . k)
+		_ -> u HFreer.:>>= Q.singleton (go HFreer.. q)
diff --git a/test/Spec.hs b/test/Spec.hs
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--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,2 @@
+main :: IO ()
+main = putStrLn "Test suite not yet implemented"
diff --git a/yaftee.cabal b/yaftee.cabal
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--- /dev/null
+++ b/yaftee.cabal
@@ -0,0 +1,62 @@
+cabal-version: 2.2
+
+-- This file has been generated from package.yaml by hpack version 0.38.1.
+--
+-- see: https://github.com/sol/hpack
+
+name:           yaftee
+version:        0.1.0.0
+synopsis:       Yet Another heFTy-inspired Extensible Effect
+description:    Please see the README on GitHub at <https://github.com/YoshikuniJujo/yaftee#readme>
+category:       Control
+homepage:       https://github.com/YoshikuniJujo/yaftee#readme
+bug-reports:    https://github.com/YoshikuniJujo/yaftee/issues
+author:         Yoshikuni Jujo
+maintainer:     yoshikuni.jujo@gmail.com
+copyright:      Copyright (c) 2025 Yoshikuni Jujo
+license:        BSD-3-Clause
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+extra-doc-files:
+    CHANGELOG.md
+
+source-repository head
+  type: git
+  location: https://github.com/YoshikuniJujo/yaftee
+
+library
+  exposed-modules:
+      Control.Monad.Yaftee.Eff
+  other-modules:
+      Paths_yaftee
+  autogen-modules:
+      Paths_yaftee
+  hs-source-dirs:
+      src
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints
+  build-depends:
+      base >=4.7 && <5
+    , ftcqueue ==0.1.*
+    , higher-order-freer-monad ==0.1.*
+    , higher-order-open-union ==0.1.*
+  default-language: Haskell2010
+
+test-suite yaftee-test
+  type: exitcode-stdio-1.0
+  main-is: Spec.hs
+  other-modules:
+      Paths_yaftee
+  autogen-modules:
+      Paths_yaftee
+  hs-source-dirs:
+      test
+  ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
+  build-depends:
+      base >=4.7 && <5
+    , ftcqueue ==0.1.*
+    , higher-order-freer-monad ==0.1.*
+    , higher-order-open-union ==0.1.*
+    , yaftee
+  default-language: Haskell2010