用地圖轉換

通常我們希望轉換或轉換集合的內容（列表或可遍歷的東西）。在 Haskell 中我們使用 map：

 -- Simple add 1
 map (+ 1) [1,2,3]
 [2,3,4]
 
 map odd [1,2,3]
 [True,False,True]
 
 data Gender = Male | Female deriving Show
 data Person = Person String Gender Int deriving Show

 -- Extract just the age from a list of people
 map (\(Person n g a) -> a) [(Person "Alex" Male 31),(Person "Ellie" Female 29)]
 [31,29]