I have been working through the exercises in Thompson's The Craft of Functional Programming 2nd Ed book. I am looking for a solution web site for Thompson's book. Or maybe the people here can help. In exercise 4.4, I am asked to define a function howManyOfFourEqual :: Int -> Int -> Int -> Int -> Int which returns the number of integers that are equal to each other. For example, howManyOfFourEqual 1 1 1 1 = 4 howManyOfFourEqual 1 2 3 1 = 2 howManyOfFourEqual 1 2 3 4 = 0 This is my solution. I give it here, since it's not an elegant solution. howManyOfFourEqual :: Int -> Int -> Int -> Int -> Int howManyOfFourEqual a b c d | a == b && howManyEqual b c d /= 0 = howManyEqual b c d + 1 | a == c && howManyEqual b c d /= 0 = howManyEqual b c d + 1 | a == d && howManyEqual b c d /= 0 = howManyEqual b c d + 1 | a == b && howManyEqual b c d == 0 = 2 | a == c && howManyEqual b c d == 0 = 2 | a == d && howManyEqual b c d == 0 = 2 | otherwise = howManyEqual b c d howManyEqual is a function from a previous exercise. howManyEqual :: Int -> Int -> Int -> Int howManyEqual a b c | a == b && b == c = 3 | a /= b && b /= c && a /= c = 0 | otherwise = 2 I hope to find a better solution. I googled but couldn't find the answer. Kaoru Hosokawa khosokawa@gmail.com