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mandlm 2016-09-22 13:30:21 +02:00
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type Peg = String
type Move = (Peg, Peg)
hanoi :: Integer -> Peg -> Peg -> Peg -> [Move]
hanoi 1 a b c = [(a, c)]
hanoi n a b c = concat [
hanoi (n-1) a c b,
hanoi 1 a b c,
hanoi (n-1) b a c ]

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This is an implementation of the Luhn Algorithm. It's used to validate
credit card numbers.
Return the last digit of an integer number
> lastDigit :: Integer -> Integer
> lastDigit n = mod n 10
Remove the last digit of an integer number and return the rest
> dropLastDigit :: Integer -> Integer
> dropLastDigit n = div n 10
Put all digits of an integer number in reverse order into a list
> toRevDigits :: Integer -> [Integer]
> toRevDigits n
> | n < 1 = []
> | otherwise = lastDigit(n) : toRevDigits(dropLastDigit(n))
Put all digits of an integer number into a list
> toDigits :: Integer -> [Integer]
> toDigits n = reverse(toRevDigits(n))
Double every second value in the input list.
> doubleEveryOther :: [Integer] -> [Integer]
> doubleEveryOther([]) = []
> doubleEveryOther(x:[]) = [x]
> doubleEveryOther(a:(b:xs)) = a : 2*b : doubleEveryOther(xs)
Sum up all digits from all integers.
> sumDigits :: [Integer] -> Integer
> sumDigits([]) = 0
> sumDigits(0:xs) = sumDigits(xs)
> sumDigits(x:xs) = lastDigit(x) + sumDigits(dropLastDigit(x) : xs)
Evaluate if a credit card number is 'valid'.
> luhn :: Integer -> Bool
> luhn x = lastDigit(sumDigits(doubleEveryOther(toRevDigits(x)))) == 0

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# CIS194
CIS194 Haskell course
CIS194 Haskell course fall 2014
http://www.seas.upenn.edu/~cis194/
http://cis.upenn.edu/~cis194/fall14/

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Compute the factorial of a given integer number n.
> fac :: Integer -> Integer
> fac 0 = 1
> fac n = n * fac(n-1)
Compute the sum of of all integer numbers from 1 to n.
> sumTo :: Integer -> Integer
> sumTo 0 = 0
> sumTo n = n + sumTo(n-1)