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tetek/card.hs

Last active November 2, 2015 20:50
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credit card validation
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card.hs
toDigits :: Integer -> [Integer]
toDigits 0 = []
toDigits a = (toDigits c) ++ [b] where (c,b) = divMod a 10
toDigitsRev = reverse . toDigits
doubleEveryOther :: [Integer] -> [Integer]
doubleEveryOther (x:y:xs) = x*2 : y : (doubleEveryOther xs)
doubleEveryOther a = a
sumDigits :: [Integer] -> Integer
sumDigits = sum . concat . map toDigits
validate :: Integer -> Bool
validate a = (==) 0 (mod (g a) 10 ) where g = sumDigits . doubleEveryOther . toDigits
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