Using guards after assigning some variables first

Question

I know I can do this...

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

But can I do something like this?

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

This will result in compilation errors, but I'm sure that you know what I'm trying to do.

Answer 1

Use a where clause instead

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

Of course, for this example we could just skip the guards and write

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