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{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE TypeFamilies #-}
module T17429
( zoomAcceptor
) where
type Zoom m = ( m ~ Emitter Int )
zoomAcceptor :: Zoom m => Emitter w a -> m w
zoomAcceptor = fmap id . zoomEmitter
zoomEmitter :: Emitter w a -> Emitter b w
zoomEmitter (Emitter go) =
Emitter $ const ([], fst $ go ())
newtype Emitter w a = Emitter (() -> ([w], [a]))
instance Functor (Emitter w) where
fmap f (Emitter go) = Emitter mapped
where
{-# INLINE mapped #-}
mapped _ = fmap f <$> go ()
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