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<code haskell A.hs>
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, DeriveGeneric #-}

module A where

import EffectCapabilities
import GHC.Generics
import {-# SOURCE #-} B

data Cap a = Cap a deriving Generic
instance Capability Cap a

instance Send BChannel Cap ()
</code>

<code haskell B.hs>
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, DeriveGeneric #-}

module B where

import EffectCapabilities
import GHC.Generics
import {-# SOURCE #-} C
import {-# SOURCE #-} A

data BChannel = BChannelV deriving Generic
instance Channel BChannel

instance Send CChannel Cap () where
         receive CChannelV () = (receive BChannelV () :: Cap ())

-- This fails because A does not send a capabitiliy with permissiom Perm to B
-- instance Send CChannel Cap SomePerm where
--          receive CChannelV SomePermV = (receive BChannelV SomePermV :: Cap SomePerm)
</code>

<code haskell C.hs>
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, DeriveGeneric #-}

module C where

import EffectCapabilities
import GHC.Generics
import A

data CChannel = CChannelV deriving Generic
instance Channel CChannel

capV :: Cap ()
capV = receive CChannelV ()
</code>

<code haskell A.hs-boot>
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}

module A where

import EffectCapabilities

data Cap a = Cap a
instance Capability Cap a
</code>

<code haskell B.hs-boot>
module B where

import EffectCapabilities

data BChannel = BChannelV
instance Channel BChannel
</code>

<code haskell C.hs-boot>
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, DeriveGeneric #-}

module C where

import EffectCapabilities
import GHC.Generics
import A

data CChannel = CChannelV deriving Generic
instance Channel CChannel

capV :: Cap ()
capV = receive CChannelV ()
</code>