Completed Chapter 1, 2, 3 and 4

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
@@ -429,9 +429,13 @@ task is to specify the type of this function.
 49
 -}
 
+squareSum :: Num a => a -> a -> a
 squareSum x y = (x + y) * (x + y)
 
 
+
+
+
 {- |
 =⚔️= Task 4
 
@@ -448,8 +452,8 @@ Implement the function that takes an integer value and returns the next 'Int'.
   every type ｡.☆.*｡. No need to worry much about "error" here, just replace the
   function body with the proper implementation.
 -}
-next :: Int -> Int
-next x = error "next: not implemented!"
+next :: Num a => a -> a
+next x = x + 1
 
 {- |
 After you've implemented the function (or even during the implementation), you
@@ -490,7 +494,8 @@ Implement a function that returns the last digit of a given number.
   whether it works for you!
 -}
 -- DON'T FORGET TO SPECIFY THE TYPE IN HERE
-lastDigit n = error "lastDigit: Not implemented!"
+lastDigit :: Integral a => a -> a
+lastDigit n = n `mod` 10
 
 
 {- |
@@ -519,8 +524,8 @@ branches because it is an expression and it must always return some value.
 👩‍🔬 Due to lazy evaluation in Haskell, only the expression from the branch
   satisfying the check will be returned and, therefore, evaluated.
 -}
-closestToZero :: Int -> Int -> Int
-closestToZero x y = error "closestToZero: not implemented!"
+closestToZero :: (Ord a, Num a) => a -> a -> a
+closestToZero x y =  if abs x < abs y then x else y
 
 
 {- |
@@ -554,7 +559,21 @@ 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 :: Ord a => a -> a -> a -> a
+mid x y z 
+    | (x <= y && y <= z) || (z <= y && y <= x) = y
+    | (y <= x && x <= z) || (z <= x && x <= y) = x
+    | otherwise = z
+
+-- mid x y z = x + y + z - minimum [x, y, z] - maximum [x, y, z]
+
+
+-- mid x y z
+--     | x > y = mid y x z
+--     | y > z = mid x z y
+--     | otherwise = y
+
+
 
 {- |
 =⚔️= Task 8
@@ -568,7 +587,9 @@ True
 >>> isVowel 'x'
 False
 -}
-isVowel c = error "isVowel: not implemented!"
+isVowel :: Char -> Bool
+isVowel c =  c `elem` "aeiouy"
+
 
 
 {- |
@@ -632,7 +653,16 @@ 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 :: Integral a => a -> a
+sumLast2 n =
+  let lastDigit = n `mod` 10
+      secondLastDigit = (n `div` 10) `mod` 10
+  in lastDigit + secondLastDigit
+
+
+
+
+
 
 
 {- |
@@ -653,7 +683,10 @@ 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 :: Integral t => t -> t
+firstDigit n
+  | n < 10    = n
+  | otherwise = firstDigit (n `div` 10)
 
 
 {-
@@ -668,3 +701,4 @@ Modules: http://learnyouahaskell.com/modules
 Let vs where: https://wiki.haskell.org/Let_vs._Where
 Packages and modules in Haskell: https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/packages.html
 -}
+