30 lines
1 KiB
Haskell
30 lines
1 KiB
Haskell
module Logic.Statement where
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import Data.Set (singleton, union, toAscList)
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data Statement
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= Atom String
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| Not Statement
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| And Statement Statement
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| Or Statement Statement
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| Implies Statement Statement
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| Iff Statement Statement
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deriving (Show, Eq)
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atoms :: Statement -> [String]
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atoms = toAscList . mkSet
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where
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mkSet (Atom key) = singleton key
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mkSet (Not s) = mkSet s
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mkSet (And s1 s2) = union (mkSet s1) (mkSet s2)
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mkSet (Or s1 s2) = union (mkSet s1) (mkSet s2)
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mkSet (Implies s1 s2) = union (mkSet s1) (mkSet s2)
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mkSet (Iff s1 s2) = union (mkSet s1) (mkSet s2)
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substatements :: Statement -> [Statement]
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substatements s@(Atom _) = [s]
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substatements s@(Not s1) = s:(substatements s1)
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substatements s@(And s1 s2) = (s:) $ substatements s1 ++ substatements s2
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substatements s@(Or s1 s2) = (s:) $ substatements s1 ++ substatements s2
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substatements s@(Implies s1 s2) = (s:) $ substatements s1 ++ substatements s2
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substatements s@(Iff s1 s2) = (s:) $ substatements s1 ++ substatements s2
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