data Sex = Female | Male

allPairs :: [(String, Sex)] -> [(String, String)]
allPairs = undefined

people :: [(String, Sex)]
people =  [("Jeff", Male), ("Britta", Female), ("Annie", Female), ("Troy", Male)]


naturalsFrom :: Integer -> [Integer]
naturalsFrom n = n : naturalsFrom (n + 1)

naturals :: [Integer]
naturals = naturalsFrom 0

-- naturals !! 2


filter' _ [] = []
filter' p (x : xs) = if p x then x : filter' p xs else filter' p xs

-- Jak se bude chovat interpret jazyka Haskell pro vstup filter' (< 3) naturals?

takeWhile' _ [] = []
takeWhile' p (x : xs) = if p x then x : takeWhile' p xs else []

-- Jak se bude chovat interpret jazyka Haskell pro vstup takeWhile' (< 3) naturals?

addNumbers :: [String] -> [String]
addNumbers = undefined

integers :: [Integer]
integers = undefined

threeSum :: [(Integer, Integer, Integer)]
threeSum = undefined


sumFold :: Num a => [a] -> a
sumFold = undefined

productFold :: Num a => [a] -> a
productFold = undefined

orFold :: [Bool] -> Bool
orFold = undefined

lengthFold :: [a] -> Int
lengthFold = undefined

maximumFold :: Ord a => [a] -> a
maximumFold = undefined


-- foldr1 (\x s -> x + 10 * s)
-- foldl1 (\s x -> 10 * s + x)


concatFold :: [[a]] -> [a]
concatFold = undefined

listifyFold :: [a] -> [[a]]
listifyFold = undefined

nullFold :: [a] -> Bool
nullFold = undefined

composeFold :: [a -> a] -> a -> a
composeFold = undefined

idFold :: [a] -> [a]
idFold = undefined

mapFold :: (a -> b) -> [a] -> [b]
mapFold = undefined

headFold :: [a] -> a
headFold = undefined

lastFold :: [a] -> a
lastFold = undefined

maxminFold :: Ord a => [a] -> (a, a)
maxminFold = undefined

suffixFold :: [a] -> [[a]]
suffixFold = undefined

filterFold :: (a -> Bool) -> [a] -> [a]
filterFold = undefined

oddEvenFold :: [a] -> ([a], [a])
oddEvenFold = undefined

takeWhileFold :: (a -> Bool) -> [a] -> [a]
takeWhileFold = undefined

dropWhileFold :: (a -> Bool) -> [a] -> [a]
dropWhileFold = undefined