data Foo
  = Bar
  | Baz
  deriving (Show)

fNot :: Foo -> Foo
fNot Baz = Bar
fNot Bar = Baz

fAnd :: Foo -> Foo -> Foo
fAnd Bar Bar = Bar
fAnd Bar Baz = Baz
fAnd Baz Bar = Baz
fAnd Baz Baz = Baz

fOr :: Foo -> Foo -> Foo
fOr Bar Bar = Bar
fOr Bar Baz = Bar
fOr Baz Bar = Bar
fOr Baz Baz = Baz

fXor :: Foo -> Foo -> Foo
fXor Bar Bar = Baz
fXor Bar Baz = Bar
fXor Baz Bar = Bar
fXor Baz Baz = Baz