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  1. {-# LANGUAGE PolyKinds  #-}
  2. {-# LANGUAGE TypeInType #-}
  3. {-# LANGUAGE TypeFamilies #-}
  4. {-# LANGUAGE GADTs #-}
  5.  
  6.  
  7. main = print "Hello"
  8.  
  9. -- type SomeSing :: * -> *
  10. data SomeSing k where 
  11.     SomeSing ::  Sing (a :: k) -> SomeSing k
  12.  
  13. data family Sing (a :: k)
  14.  
  15. class SingKind k where
  16.   fromSing :: Sing (a :: k) -> k
  17.   toSing   :: k -> SomeSing k
  18.  
  19. -----
  20.  
  21. data instance Sing (a :: Bool) where 
  22.    STrue  :: Sing True
  23.    SFalse :: Sing False
  24.  
  25. instance SingKind Bool where
  26.   fromSing s = case s of
  27.     STrue  -> True
  28.     SFalse -> False
  29.  
  30.   toSing b = case b of
  31.     True  -> SomeSing STrue
  32.     False -> SomeSing SFalse
  33.  
  34.  
Success #stdin #stdout 0s 4812KB
comments (?)
stdin 
Standard input is empty
stdout 
"Hello"
https://ideone.com/QD1inW
language:
Haskell (ghc 8.4.4)
created:
4 years ago
visibility:
public

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