Day2

type Student = (String, Int)
s1 :: Student
s2 :: Student
s1 = ("Ivan Petrov", 111213)
s2 = ("Hristo Hristov", 102030)

mult4 :: (Int, Int, Int, Int) -> Int
mult4 (x, y, z, t) = x*y*z*t

sort2 :: (Int, Int) -> (Int, Int)
sort2 (x, y) = if x >= y then (x, y) else (y, x)

fib :: Int -> Int
fib n
    | n == 1 = 1
    | n == 2 = 1
    | n > 2  = fib (n-2) + fib (n-1)
    | otherwise = error "Not defined"

fibStep :: (Int, Int) -> (Int, Int)
fibStep (u, v) = (u, u+v)


fibPair :: Int -> (Int, Int)
fibPair n = (fib(n), fib(n + 1))

toEnd :: a -> [a] -> [a]
toEnd x l = l ++ [x]

sumPairs :: [(Int, Int)] -> [Int]
sumPairs pL = [x + y | (x, y) <- pL]

digit :: Char -> Bool
digit ch = ch >= '0' && ch <= '9'

all_digits :: String -> String
all_digits str = [ch | ch <- str,  digit ch]

allEven :: [Int] -> Bool
allEven x = (x == [a | a <- x, even a])

allOdd :: [Int] -> Bool
allOdd x = (x == [a | a <- x, odd a])

revWords :: String -> String
revWords input = (unwords . reverse . words) input

sumMy :: [Int] -> Int
sumMy [] = 0
sumMy (x:xs) = x + sum xs

concatMy :: [[a]] -> [a]
concatMy [] = []
concatMy (x : xs) = x ++ concat xs

calssify :: Int -> String
classify age = case age of 0 -> "newborn"
                           1 -> "infant"
                           2 -> "toddler"
                           _ -> "senior citizen"

day :: Int -> String
day x = case x of
                1 -> "Monday"
                2 -> "Tuesday"
                3 -> "Wednesday"
                4 -> "Thursday"
                5 -> "Friday"
                6 -> "Saturday"
                7 -> "Sunday"
                _ -> "Not defined"