gistfile1.hs

factorial1 n = if n == 0 then 1 else n * factorial1 (n-1)

factorial2 0 = 1
factorial2 n = n * factorial2 (n-1)

factorial3 n = foldr (*) 1 [1..n]

factorial4 = foldr (*) 1 . enumFromTo 1



sumList [] = 0
sumList (x:xs) = x + sumList xs

lenList [] = 0
lenList (_:xs) = 1 + lenList xs

sumPositive [] = 0
sumPositive (x:xs) | x > 0 = x + sumPositive xs
sumPositive (_:xs) = sumPositive xs



qsort [] = []
qsort (x:xs) = qsort [y | y <- xs, y < x] ++ [x] ++ qsort [y | y <- xs, y >= x]



primes = 2 : [ k | k <- [3..], isPrime k ]

isPrime k = all (\n -> k `mod` n /= 0) $ takeWhile (\n -> n^2 <= k) primes


fibonacci = 1 : 1 : zipWith (+) fibonacci (tail fibonacci)