jkr2255 / prop_logic

module PropLogic

  class Constant < Variable

    def variables

      []

    end

    def to_cnf

      self

    end

  end

  class TrueConstant < Constant

    include Singleton

    def to_s(*)

      'true'

    end

    def assign(trues, falses, variables = nil)

      if falses.include?(self)

        raise ArgumentError, 'Contradicted assignment'

      end

      self

    end

  end

  class FalseConstant < Constant

    def assign(trues, falses, variables = nil)

      if trues.include?(self)

        raise ArgumentError, 'Contradicted assignment'

      end

      self

    end

  end

  True = TrueConstant.instance.freeze

  False = FalseConstant.instance.freeze

end