# File lib/parslet/cause.rb, line 48
    def to_s
      line, column = source.line_and_column(pos)
      # Allow message to be a list of objects. Join them here, since we now
      # really need it. 
      Array(message).map { |o| 
        o.respond_to?(:to_slice) ? 
          o.str.inspect : 
          o.to_s }.join + " at line #{line} char #{column}."
    end