module SatDef where

data P a = Var a
         | Not (P a)
         | P a :&: P a
         | P a :|: P a
    deriving (Eq, Show)
infixr 3 :&:
infixr 2 :|:

-- Structural recursion so you don't have to repeat it all the time!
foldP :: (a -> r) -> (r -> r) -> (r -> r -> r) -> (r -> r -> r) -> P a -> r
foldP var neg and or = go
  where
    go (Var a) = var a
    go (Not p) = neg (go p)
    go (p :&: q) = and (go p) (go q)
    go (p :|: q) = or (go p) (go q)