打印数据类型 - Haskell

Question

data Person = Person { firstName :: String
                     , lastName :: String
                     , age :: Int
                     } deriving (Show)


buffy = Person "Buffy" "Summers" 22
burt = Person "Burt" "Reynolds" 23
cloud = Person "Cloud" "Strife" 22
rick = Person "Rick" "Sanchez" 21

people = [buffy,burt,cloud,rick]

我正在寻找多种方法来打印firstName列表中每个元素的people个。

打印这些元素可以采用以下形式打印：

• x1,x2,x3,...xn

• [x1,x2,x3,...xn]

• 多行：

  x1  
  x2   
  x3   
  ...  
  xn
  

Answer 1

如果您创建类似Person的记录类型，则会获得以下字段选择器：

firstName :: Person -> String
lastName :: Person -> String
age :: Person -> Int

因此，您可以map firstName覆盖列表，将[Person]变为[String]。

然后，打印firstName只是mapM_ (putStrLn . firstName) people。