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+-- This are my solutions to the exercises from https://github.com/moocfi/haskell-mooc
+
+import Data.List
+
+---------
+-- Set.01
+-- https://github.com/moocfi/haskell-mooc/blob/master/exercises/Set1.hs
+
+-- Ex. 1
+
+one :: Integer -- function declaration: types of arguments and output
+one = 1        -- function definition
+
+two :: Integer
+two = 2
+
+-- Ex. 2
+
+double :: Integer -> Integer
+double x = x * 2
+
+-- Ex. 3
+
+quadruple :: Integer -> Integer
+quadruple x = double (double x)
+
+-- Ex. 4 
+
+distance :: Double -> Double -> Double -> Double -> Double
+-- exponentiation operator: ^ for integers, ^^ for fractionals and ** for floating point
+distance x1 y1 x2 y2 = sqrt (abs(x1 - x2)**2 + abs(y1 - y2)**2)
+
+-- Ex. 5
+
+eeny :: Integer -> String
+eeny x = if even x 
+         then "eeny" 
+         else "meeny"
+
+-- Ex. 6
+
+checkPassword :: String -> String
+checkPassword password = if password == "swordfish" || password == "mellon"
+                         then "You're in."
+                         else "ACCESS DENIED!"
+
+-- Ex. 7
+
+postagePrice :: Int -> Int
+postagePrice weight = if weight > 5000 then 6000
+                      else if weight > 500 then 300 + weight * 1
+                      else 250
+
+-- Ex. 8
+
+isZero :: Int -> Bool
+isZero 0 = True -- this is pattern matching
+isZero x = False
+
+-- Ex. 9
+
+sumTo :: Int -> Int
+sumTo 1 = 1
+sumTo n = n + sumTo (n - 1)
+
+-- Ex. 10
+
+power :: Int -> Int -> Int
+power n 1 = n
+power n k = n * power n (k - 1)
+
+-- Ex. 11
+
+ilog3 :: Int -> Int
+ilog3 0 = 0
+ilog3 n = 1 + ilog3 (div n 3)
+
+----------
+-- Set.02a
+-- https://github.com/moocfi/haskell-mooc/blob/master/exercises/Set2a.hs
+
+-- Functions you'll need: head, tail, take, drop, length, null
+
+-- Ex. 1
+
+years = [1982, 2004, 2020]
+
+-- Ex. 2
+
+takeFinal :: Int -> [a] -> [a] -- a is the Haskell equivalent of generics (T) in C#
+takeFinal n xs
+    | n > length xs = xs
+    | otherwise = drop (length xs - n) xs
+
+-- Ex. 3
+
+updateAt :: Int -> a -> [a] -> [a]
+-- elements before i + x + elemenets after i ; ++ concatenates arrays
+updateAt i x xs = take i xs ++ [x] ++ drop (i + 1) xs 
+
+-- Ex. 4
+
+substring :: Int -> Int -> String -> String
+substring i j s = drop i (take j s)
+
+-- Ex. 5
+
+isPalindrome :: String -> Bool
+isPalindrome s = s == reverse s
+
+-- Ex. 6
+
+palindromify :: String -> String
+palindromify s = if isPalindrome s then s -- can easily make it: if s == reverse s then s , but decided this way was more readable
+                 else palindromify (take (length s - 2) (drop 1 s))
+
+-- Ex. 7
+
+safeDiv :: Int -> Int -> String
+safeDiv x y
+    | y == 0 = "Nothing"
+    | otherwise = "Just " ++ show (div x y) -- show casts the value to string
+
+-- Ex. 8
+
+greet :: String -> Maybe String -> String -- maybe means the value can (String) or can not be given (Nothing) ; you need to use pattern matching
+greet firstName Nothing = "Hello, " ++ firstName ++ "!"
+greet firstName (Just lastName) = "Hello, " ++ firstName ++ " " ++ lastName ++ "!"
+
+-- Ex. 9
+
+safeIndex :: [a] -> Int -> Maybe a
+safeIndex xs i = if 0 > i || i >= length xs then Nothing
+                 else Just (xs !! i)
+
+-- Ex. 10
+
+eitherDiv :: Int -> Int -> Either String Int -- a value can be the left one or the right one (specified when given)
+eitherDiv x 0 = Left (show x ++ "/0")
+eitherDiv x y = Right (div x y)
+
+-- Ex. 11
+
+addEithers :: Either String Int -> Either String Int -> Either String Int
+addEithers (Right x) (Right y) = Right (x + y)
+addEithers (Right x) (Left y)  = Left y
+addEithers (Left x)  (Right y) = Left x