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  1. import Prelude hiding ((&&), (||), not)
  2. import qualified Prelude
  3.  
  4. infixr 3  &&
  5. infixr 2  ||
  6. infixr 3  `xor`
  7.  
  8. class Boolean a where
  9.     (&&) :: a -> a -> a
  10.     (||) :: a -> a -> a
  11.     not :: a -> a
  12.  
  13. data Trivalent = TriFalse | TriUnknown | TriTrue deriving (Show, Eq, Ord)
  14.  
  15. instance Boolean Trivalent where
  16.     TriFalse && _ = TriFalse
  17.     _ && TriFalse = TriFalse
  18.     TriTrue && TriTrue = TriTrue
  19.     _ && _ = TriUnknown
  20.     TriTrue || _ = TriTrue
  21.     _ || TriTrue = TriTrue
  22.     TriFalse || TriFalse = TriFalse
  23.     _ || _ = TriUnknown
  24.     not TriTrue = TriFalse
  25.     not TriFalse = TriTrue
  26.     not TriUnknown = TriUnknown
  27.  
  28. instance Boolean Bool where
  29.     (&&) = (Prelude.&&)
  30.     (||) = (Prelude.||)
  31.     not = Prelude.not
  32.  
  33. xor :: Boolean a => a -> a -> a
  34. a `xor` b = not a && b || not b && a
  35.  
  36. main = do
  37.     print $ TriTrue && TriFalse
  38.     print $ not (TriFalse || TriUnknown)
  39.     print $ not (TriUnknown || TriFalse && TriTrue)
  40.     print $ 2 < 3 `xor` False
  41.     print $ map (&& TriTrue) [TriTrue, TriFalse, TriUnknown]
  42.     print $ map (&& True) [True, False]
  43.  
Success #stdin #stdout 0.02s 3540KB
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Standard input is empty
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TriFalse
TriUnknown
TriUnknown
True
[TriTrue,TriFalse,TriUnknown]
[True,False]
https://ideone.com/rXQ0lw
language:
Haskell (ghc 8.4.4)
created:
13 years ago
visibility:
public

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