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{-# LANGUAGE TypeFamilies, ConstraintKinds #-}
import qualified Data.Set as S
import GHC.Exts ( Constraint )
class RMonad m where
type RMonadCtxt m a :: Constraint
returnR :: (RMonadCtxt m a) => a -> m a
bindR :: (RMonadCtxt m a, RMonadCtxt m b) => m a -> (a -> m b) -> m b
instance RMonad [] where
type RMonadCtxt [] a = ()
returnR x = [x]
bindR = flip concatMap
instance RMonad S.Set where
type RMonadCtxt S.Set a = Ord a
returnR x = S.singleton x
bindR mx fxmy = S.fromList [y | x <- S.toList mx, y <- S.toList (fxmy x)]
main = do
print $ (returnR 1 ++ returnR 2) `bindR`
(\x -> returnR (x + 1) ++ returnR (x + 2))
print $ (returnR 1 `S.union` returnR 2) `bindR`
(\x -> returnR (x + 1) `S.union` returnR (x + 2))
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