expression_problem.rb

class Number < Struct.new(:value)
  def print
    value
  end
end

class Binary < Struct.new(:left, :right)
end

class Plus < Binary
  def print
    "(#{left.print} + #{right.print})"
  end
end

class Times < Binary
  def print
    "(#{left.print} * #{right.print})"
  end
end

expression = Plus.new(
  Number.new(1),
  Times.new(Number.new(2), Number.new(5))
)

puts expression.print




class Negation < Struct.new(:expression)
  def print
    "-#{expression.print}"
  end
end

expression = Plus.new(
  Number.new(1),
  Times.new(Number.new(2), Negation.new(Number.new(5)))
)

puts expression.print


# dev3

# jankos_evaluations

class Number
  def eval
    value
  end
end

class Plus
  def eval
    left.eval + right.eval
  end
end

class Times
  def eval
    left.eval * right.eval
  end
end

class Negation
  def eval
    -expression.eval
  end
end


puts expression.eval