首先分配一些变量后使用警卫

Question

我知道我能做到这一点......

isZero :: Int -> Bool
isZero x
  | x == 0      = True
  | otherwise   = False

但我可以这样做吗？

isPalindrome :: Int -> Bool
isPalindrome x
  let digitList = intToDigits x -- Decomposes the integer into
                                -- digits, i.e. 37 -> [3, 7]
  | digitList == reverse digitList                = True
  | otherwise                                     = False

这将导致编译错误,但我确信你知道我正在尝试做什么.

Answer 1

请改用where子句

isPalindrome :: Int -> Bool
isPalindrome x
    | digitList == reverse digitList = True
    | otherwise                      = False
    where digitList = intToDigits x

当然,对于这个例子,我们可以跳过警卫并写下来

isPalindrome x = digitList == reverse digitList
    where digitList = intToDigits x