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26 lines
827 B
Haskell
26 lines
827 B
Haskell
{-# LANGUAGE UndecidableInstances #-}
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module Control.Monad.Stateless
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( MonadStateless(..)
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) where
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import Prelude
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import Control.Monad.Trans.Control
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import Data.Type.Equality
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class (MonadBaseControl b m, forall a. StatelessProof m a) => MonadStateless b m | m -> b where
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liftWithStateless :: ((forall a. m a -> b a) -> b c) -> m c
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instance (MonadBaseControl b m, forall a. StatelessProof m a) => MonadStateless b m where
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liftWithStateless f = liftBaseWith $ \lowerBase ->
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let lowerBasePure :: forall a. m a -> b a
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lowerBasePure m = case statelessProof @m @a of
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Refl -> lowerBase m
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in f lowerBasePure
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class (StM m a ~ a) => StatelessProof m a where
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statelessProof :: StM m a :~: a
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instance (StM m a ~ a) => StatelessProof m a where
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statelessProof = Refl
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