检索元组并在第n个元素上进行操作

Question

我有一个定义的类型和这种类型的元素。这个元素有元组，我需要取3个该元组并取平均值。

type Name = String
type Subject = String
type Grade = Float

-- Definition of a type
type Student = (Name, Subject, Grade, Grade, Grade)

-- Elements of this type
student :: Int -> Student
student 1 = ("Rafael", "INE5416", 6.0, 5.0, 8.0)

-- now i need a function that can receive an Int as student ID, get this
-- student by ID and calculate her average grade.
getAverage :: Int -> Float
getAverage student x =  ((_, _, c, d, e) / 3) -- Int is to get x student

main = do
  print (getAverage(1)) -- passing student ID--

Answer 1

您可以使用给定的ID号对student进行调用，以进行模式匹配，然后获取您所关心的术语的平均值。

getAverage :: Int -> Float
getAverage studentId = (a + b + c) / 3
  where (_, _, a, b, c) = student studentId

危险是student功能不完整。目前评估student 2会使程序崩溃。