Solutions for Chapter 1,2 & 3

.gitignore

@@ -54,3 +54,17 @@ TAGS
 # other
 .DS_Store
 .env
+/out/production/learn4haskell/Chapter1.hs
+/out/production/learn4haskell/Chapter2.hs
+/out/production/learn4haskell/Chapter3.hs
+/out/production/learn4haskell/Chapter4.hs
+/out/test/learn4haskell/Test/Chapter1.hs
+/out/test/learn4haskell/Test/Chapter2.hs
+/out/test/learn4haskell/Test/Chapter3.hs
+/out/test/learn4haskell/Test/Chapter4.hs
+/out/test/learn4haskell/DoctestChapter1.hs
+/out/test/learn4haskell/DoctestChapter2.hs
+/out/test/learn4haskell/DoctestChapter3.hs
+/out/test/learn4haskell/DoctestChapter4.hs
+/out/test/learn4haskell/Spec.hs
+/stack.yaml

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
@@ -489,9 +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 = abs n `mod` 10
 
 {- |
 =⚔️= Task 6
@@ -520,7 +519,7 @@ 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 +552,11 @@ 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 && y <= z = y
+  | x >= y && y >= z = y
+  | otherwise = mid y z x
 
 {- |
 =⚔️= Task 8
@@ -568,7 +570,19 @@ True
 >>> isVowel 'x'
 False
 -}
-isVowel c = error "isVowel: not implemented!"
+isVowel :: Char -> Bool
+isVowel c
+  | c == 'a' = True
+  | c == 'e' = True
+  | c == 'i' = True
+  | c == 'o' = True
+  | c == 'u' = True
+  | c == 'A' = True
+  | c == 'E' = True
+  | c == 'I' = True
+  | c == 'O' = True
+  | c == 'U' = True
+  | otherwise = False
 
 
 {- |
@@ -631,9 +645,12 @@ 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 = (lastDigit n) + secondLastDigit
+  where
+    lastTwo = (mod (abs n) 100)
+    lastD = lastDigit n
+    secondLastDigit = (lastTwo - lastD) `div` 10
 
 {- |
 =💣= Task 10*
@@ -652,9 +669,12 @@ 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 
+  | absN < 10  = absN
+  | otherwise = firstDigit (div absN 10)
+  where
+    absN = abs n      
 
 {-
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