第2章 練習問題 G

• showDate :: Date -> String を定義せよ

  type Year  = Int
  type Month = Int
  type Day   = Int
  
  type Date  = (Day, Month, Year)
  
  showDate :: Date -> String
  showDate (d, m, y) = show d ++ suffix d ++ " "
                    ++ months !! (m - 1) ++ ", " ++ show y
  
  months = [ January, Feburary, March, April
           , May, June, July, August
           , September, October, November, December
           ]