Completed Chapter 1 and Chapter 2

src/Chapter1.hs

@@ -209,31 +209,31 @@ So, the output in this example means that 'False' has type 'Bool'.
 > Try to guess first and then compare your expectations with GHCi output
 
 >>> :t True
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+True :: Bool
 >>> :t 'a'
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+'a' :: Char
 >>> :t 42
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+42 :: Num a => a
 
 A pair of boolean and char:
 >>> :t (True, 'x')
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+(True, 'x') :: (Bool, Char)
 
 Boolean negation:
 >>> :t not
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+not :: Bool -> Bool
 
 Boolean 'and' operator:
 >>> :t (&&)
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+(&&) :: Bool -> Bool -> Bool
 
 Addition of two numbers:
 >>> :t (+)
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+(+) :: Num a => a -> a -> a
 
 Maximum of two values:
 >>> :t max
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+max :: Ord a => a -> a -> a
 
 You might not understand each type at this moment, but don't worry! You've only
 started your Haskell journey. Types will become your friends soon.
@@ -301,43 +301,43 @@ expressions in GHCi
   functions and operators first. Remember this from the previous task? ;)
 
 >>> 1 + 2
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+3
 
 >>> 10 - 15
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+-5
 
 >>> 10 - (-5)  -- negative constants require ()
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+15
 
 >>> (3 + 5) < 10
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+True
 
 >>> True && False
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+False
 
 >>> 10 < 20 || 20 < 5
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+True
 
 >>> 2 ^ 10  -- power
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+1024
 
 >>> not False
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+True
 
 >>> div 20 3  -- integral division
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+6
 
 >>> mod 20 3  -- integral division remainder
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+2
 
 >>> max 4 10
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+10
 
 >>> min 5 (max 1 2)
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+2
 
 >>> max (min 1 10) (min 5 7)
-<INSERT THE RESULT INSTEAD OF THE TEXT>
+5
 
 Because Haskell is a __statically-typed__ language, you see an error each time
 you try to mix values of different types in situations where you are not
@@ -428,7 +428,7 @@ task is to specify the type of this function.
 >>> squareSum 3 4
 49
 -}
-
+squareSum :: Int -> Int -> Int
 squareSum x y = (x + y) * (x + y)
 
 
@@ -449,7 +449,7 @@ Implement the function that takes an integer value and returns the next 'Int'.
   function body with the proper implementation.
 -}
 next :: Int -> Int
-next x = error "next: not implemented!"
+next x = x + 1
 
 {- |
 After you've implemented the function (or even during the implementation), you
@@ -489,8 +489,8 @@ Implement a function that returns the last digit of a given number.
   results. Or you can try to guess the function name, search for it and check
   whether it works for you!
 -}
--- DON'T FORGET TO SPECIFY THE TYPE IN HERE
-lastDigit n = error "lastDigit: Not implemented!"
+lastDigit :: Int -> Int
+lastDigit n = mod (abs n) 10
 
 
 {- |
@@ -520,7 +520,7 @@ branches because it is an expression and it must always return some value.
   satisfying the check will be returned and, therefore, evaluated.
 -}
 closestToZero :: Int -> Int -> Int
-closestToZero x y = error "closestToZero: not implemented!"
+closestToZero x y = if abs x < abs y then x else y
 
 
 {- |
@@ -553,8 +553,12 @@ value after "=" where the condition is true.
 
 Casual reminder about adding top-level type signatures for all functions :)
 -}
-
-mid x y z = error "mid: not implemented!"
+mid :: Int -> Int -> Int -> Int
+mid x y z
+  | (x > y && x < z) || (x < y && x > z) = x
+  | (y > x && y < z) || (y < x && y > z) = y
+  | (z > x && z < y) || (z < x && z > y) = z
+  | otherwise = if x == y then x else z
 
 {- |
 =⚔️= Task 8
@@ -568,7 +572,14 @@ True
 >>> isVowel 'x'
 False
 -}
-isVowel c = error "isVowel: not implemented!"
+isVowel :: Char -> Bool
+isVowel c
+  | c == 'a' || c == 'A' = True
+  | c == 'e' || c == 'E' = True
+  | c == 'i' || c == 'I' = True
+  | c == 'o' || c == 'O' = True
+  | c == 'u' || c == 'U' = True
+  | otherwise = False
 
 
 {- |
@@ -631,9 +642,11 @@ Implement a function that returns the sum of the last two digits of a number.
 Try to introduce variables in this task (either with let-in or where) to avoid
 specifying complex expressions.
 -}
-
-sumLast2 n = error "sumLast2: Not implemented!"
-
+sumLast2 :: Int -> Int
+sumLast2 n = 
+  let (remaining, last1) = divMod (abs n) 10
+      last2 = mod remaining 10
+  in (last1 + last2)
 
 {- |
 =💣= Task 10*
@@ -652,8 +665,8 @@ Implement a function that returns the first digit of a given number.
 You need to use recursion in this task. Feel free to return to it later, if you
 aren't ready for this boss yet!
 -}
-
-firstDigit n = error "firstDigit: Not implemented!"
+firstDigit :: Int -> Int
+firstDigit n = if abs n < 10 then abs n else firstDigit (div n 10)
 
 
 {-

src/Chapter2.hs

@@ -136,43 +136,43 @@ functions in GHCi and insert the corresponding resulting output below:
 
 List of booleans:
 >>> :t [True, False]
-
+[True, False] :: [Bool]
 
 String is a list of characters:
 >>> :t "some string"
-
+"some string" :: [Char]
 
 Empty list:
 >>> :t []
-
+[] :: [a]
 
 Append two lists:
 >>> :t (++)
-
+(++) :: [a] -> [a] -> [a]
 
 Prepend an element at the beginning of a list:
 >>> :t (:)
-
+(:) :: a -> [a] -> [a]
 
 Reverse a list:
 >>> :t reverse
-
+reverse :: [a] -> [a]
 
 Take first N elements of a list:
 >>> :t take
-
+take :: Int -> [a] -> [a]
 
 Create a list from N same elements:
 >>> :t replicate
-
+replicate :: Int -> a -> [a]
 
 Split a string by line breaks:
 >>> :t lines
-
+lines :: String -> [String]
 
 Join a list of strings with line breaks:
 >>> :t unlines
-
+unlines :: [String] -> String
 
 -}
 
@@ -186,31 +186,31 @@ Evaluate the following expressions in GHCi and insert the answers. Try
 to guess first, what you will see.
 
 >>> [10, 2] ++ [3, 1, 5]
-
+[10,2,3,1,5]
 >>> [] ++ [1, 4]  -- [] is an empty list
-
+[1,4]
 >>> 3 : [1, 2]
-
+[3,1,2]
 >>> 4 : 2 : [5, 10]  -- prepend multiple elements
-
+[4,2,5,10]
 >>> [1 .. 10]  -- list ranges
-
+[1,2,3,4,5,6,7,8,9,10]
 >>> [10 .. 1]
-
+[]
 >>> [10, 9 .. 1]  -- backwards list with explicit step
-
+[10,9,8,7,6,5,4,3,2,1]
 >>> length [4, 10, 5]  -- list length
-
+3
 >>> replicate 5 True
-
+[True,True,True,True,True]
 >>> take 5 "Hello, World!"
-
+"Hello"
 >>> drop 5 "Hello, World!"
-
+", World!"
 >>> zip "abc" [1, 2, 3]  -- convert two lists to a single list of pairs
-
+[('a',1),('b',2),('c',3)]
 >>> words "Hello   Haskell     World!"  -- split the string into the list of words
-
+["Hello","Haskell","World!"]
 
 
 👩‍🔬 Haskell has a lot of syntax sugar. In the case with lists, any
@@ -336,7 +336,9 @@ from it!
 ghci> :l src/Chapter2.hs
 -}
 subList :: Int -> Int -> [a] -> [a]
-subList = error "subList: Not implemented!"
+subList start end list
+    | start < 0 || end < 0 || end < start = []
+    | otherwise = drop start (take (end + 1) list)
 
 {- |
 =⚔️= Task 4
@@ -348,8 +350,8 @@ Implement a function that returns only the first half of a given list.
 >>> firstHalf "bca"
 "b"
 -}
--- PUT THE FUNCTION TYPE IN HERE
-firstHalf l = error "firstHalf: Not implemented!"
+firstHalf :: [a] -> [a]
+firstHalf l = take (div (length l) 2) l
 
 
 {- |
@@ -501,7 +503,9 @@ True
 >>> isThird42 [42, 42, 0, 42]
 False
 -}
-isThird42 = error "isThird42: Not implemented!"
+isThird42 :: [Int] -> Bool
+isThird42 (_:_:42:_) = True
+isThird42 _ = False
 
 
 {- |
@@ -606,7 +610,8 @@ Implement a function that duplicates each element of the list
 
 -}
 duplicate :: [a] -> [a]
-duplicate = error "duplicate: Not implemented!"
+duplicate [] = []
+duplicate (x:xs) = x : x : duplicate xs
 
 
 {- |
@@ -621,7 +626,10 @@ Write a function that takes elements of a list only in even positions.
 >>> takeEven [2, 1, 3, 5, 4]
 [2,3,4]
 -}
-takeEven = error "takeEven: Not implemented!"
+takeEven :: [a] -> [a]
+takeEven [] = []
+takeEven (x:_:xs) = x : takeEven xs
+takeEven (x:xs) = x : takeEven xs
 
 {- |
 =🛡= Higher-order functions
@@ -728,7 +736,7 @@ value of the element itself
 🕯 HINT: Use combination of 'map' and 'replicate'
 -}
 smartReplicate :: [Int] -> [Int]
-smartReplicate l = error "smartReplicate: Not implemented!"
+smartReplicate l = concat (map (\x -> replicate x x) l)
 
 {- |
 =⚔️= Task 9
@@ -741,7 +749,8 @@ the list with only those lists that contain a passed element.
 
 🕯 HINT: Use the 'elem' function to check whether an element belongs to a list
 -}
-contains = error "contains: Not implemented!"
+contains :: (Foldable t, Eq a) => a -> [t a] -> [t a]
+contains n l = filter (elem n ) l
 
 
 {- |
@@ -781,12 +790,14 @@ Let's now try to eta-reduce some of the functions and ensure that we
 mastered the skill of eta-reducing.
 -}
 divideTenBy :: Int -> Int
-divideTenBy x = div 10 x
+divideTenBy = div 10
 
 -- TODO: type ;)
-listElementsLessThan x l = filter (< x) l
+listElementsLessThan :: Int -> [Int] -> [Int]
+listElementsLessThan x = filter (< x)
 
 -- Can you eta-reduce this one???
+pairMul :: [Int] -> [Int] -> [Int]
 pairMul xs ys = zipWith (*) xs ys
 
 {- |
@@ -842,7 +853,11 @@ list.
 
 🕯 HINT: Use the 'cycle' function
 -}
-rotate = error "rotate: Not implemented!"
+rotate :: Int -> [a] -> [a]
+rotate n l
+  | n < 0 = []
+  | n == 0 = l
+  | otherwise = take (length l) (drop (n `mod` (length l)) (cycle l))
 
 {- |
 =💣= Task 12*
@@ -858,7 +873,12 @@ and reverses it.
   function, but in this task, you need to implement it manually. No
   cheating!
 -}
-rewind = error "rewind: Not Implemented!"
+rewind :: [a] -> [a]
+rewind l = go l []
+  where
+    go :: [a] -> [a] -> [a]
+    go [] z = z
+    go (x:xs) z = go xs (x:z)
 
 
 {-