def push(arg)
      if arg.is_a? Symbol
        stack.push scope.get_var(arg)
      elsif arg.is_a?(Fixnum) || arg.is_a?(Float)
        stack.push Types::Number.new(arg)
      elsif arg.is_a?(String)
        stack.push Types::String.new(arg)
      end
    end
def push(arg)
      if arg.is_a? Symbol
        stack.push scope.get_var(arg)
      elsif arg.is_a?(Fixnum) || arg.is_a?(Float)
        stack.push Types::Number.new(arg)
      elsif arg.is_a?(String)
        stack.push Types::String.new(arg)
      end
    end
instructions