Haskell - 函数式编程技巧(练习 4.3)

Question

我有以下问题(Haskell - 函数式编程的技巧):

Give a definition of the function

howManyEqua1 :: Int -> Int -> Int -> Int

which returns how many of its three arguments are equal, so that

howManyEqua1 :: 34 25 36 = 0
howManyEqual :: 34 25 34 = 2
howManyEqual :: 34 34 34 = 3

我给出的答案是:

howManyEqual :: Int -> Int -> Int -> Int
howManyEqual    a      b      c
    | a == b && b == c            = 3
    | a == b                      = 2
    | b == c                      = 2
    | a == c                      = 2
    | otherwise                   = 0

但是，我相信有更好的分类方法，但不确定如何分类。

Answer 1

怎么样:

howManyEqual a b c
    | a == b && b == c           = 3
    | a /= b && a /= c && b /= c = 0
    | otherwise                  = 2