http://www.seas.upenn.edu/~cis194/spring13/hw/01-intro.pdf

gistfile1.hs

-- CIS 194: Homework 1 (http://www.seas.upenn.edu/~cis194/hw/01-intro.pdf)

-- Part I - Credit Card Validation
toDigits :: Integer -> [Integer]
toDigits n
       | n <= 0    = []
       | otherwise = toDigits (n `div` 10) ++ [n `mod` 10]

toDigitsRev :: Integer -> [Integer]
toDigitsRev = reverse . toDigits

doubleEveryTwo :: [Integer] -> [Integer]
doubleEveryTwo []         = []
doubleEveryTwo (x:[])     = [x]
doubleEveryTwo (x:(y:zs)) = [x] ++ [2 * y] ++ doubleEveryTwo zs

doubleEveryOther :: [Integer] -> [Integer]
doubleEveryOther = reverse . doubleEveryTwo . reverse

sumDigits :: [Integer] -> Integer
sumDigits =  sum . concatMap toDigits

validate :: Integer -> Bool
validate = (==0) . (`mod` 10) . sumDigits . doubleEveryOther . toDigits

-- Part II - Hanoi Tower
type Peg = String
type Move = (Peg, Peg)

hanoi :: Integer -> Peg -> Peg -> Peg -> [Move]
hanoi 0 _ _ _ = []
hanoi n a b c = hanoi (n-1) a c b ++ [(a,b)] ++ hanoi (n-1) c b a

main = do putStrLn "Credit card validation"
          print $ toDigits 1234
          print $ toDigitsRev 1234
          print $ toDigits 0
          print $ toDigits (-17)
          print $ doubleEveryOther [8,7,6,5]
          print $ doubleEveryOther [1,2,3]
          print $ sumDigits [16,7,12,5]
          print $ validate 4012888888881881
          print $ validate 4012888888881882
          putStrLn "---------------------"
          putStrLn "Hanoi tower"
          print $ hanoi 2 "a" "b" "c"