def empty_exp?(exp)
      case exp[0]
      when :multi
        exp[1..-1].all? {|e| empty_exp?(e) }
      when :newline
        true
      else
        false
      end
    end
def empty_exp?(exp)
      case exp[0]
      when :multi
        exp[1..-1].all? {|e| empty_exp?(e) }
      when :newline
        true
      else
        false
      end
    end
Check if expression is empty

 @param exp [Array] Temple expression
 @return true if expression is empty