Completed Chapter 2

CHANGELOG.md.save0

@@ -0,0 +1,11 @@
+# Changelog
+
+`learn4haskell` uses [PVP Versioning][1].
+The changelog is available [on GitHub][2].
+
+## 0.0.0.0
+
+* Initially created.
+
+[1]: https://pvp.haskell.org
+[2]: https://github.com/kowainik/learn4haskell/releases

Makefile

@@ -49,3 +49,6 @@ test-chapter4-basic:
 .PHONY: test-all
 test-all:
 	cabal test all --enable-tests --test-show-details=direct
+
+ghcup-list:
+	ghcup list -c set

app/Main.hs

@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = putStrLn "Hello, Haskell!"

learn4haskell-yebowhatsay.cabal.xxx

@@ -0,0 +1,37 @@
+cabal-version:      2.4
+name:               learn4haskell-yebowhatsay
+version:            0.1.0.0
+
+-- A short (one-line) description of the package.
+-- synopsis:
+
+-- A longer description of the package.
+-- description:
+
+-- A URL where users can report bugs.
+-- bug-reports:
+
+-- The license under which the package is released.
+-- license:
+author:             yebowhatsay
+maintainer:         [email protected]
+
+-- A copyright notice.
+-- copyright:
+-- category:
+extra-source-files:
+    README.md
+    CHANGELOG.md
+
+executable learn4haskell-yebowhatsay
+    main-is:          Main.hs
+
+    -- Modules included in this executable, other than Main.
+    -- other-modules:
+
+    -- LANGUAGE extensions used by modules in this package.
+    -- other-extensions:
+    build-depends:    base 
+    --^>=4.13.0.0
+    hs-source-dirs:   app
+    default-language: Haskell2010

learn4haskell.cabal

@@ -22,7 +22,8 @@ source-repository head
   location:            https://github.com/kowainik/learn4haskell.git
 
 common common-options
-  build-depends:       base ^>= 4.14.0.0
+  build-depends:       base 
+  --^>= 4.14.0.0
 
   ghc-options:         -Wall
                        -Wcompat
@@ -42,7 +43,8 @@ common common-options
 common common-doctest
   import:              common-options
   hs-source-dirs:      test
-  build-depends:       doctest ^>= 0.17
+  build-depends:       doctest 
+  --^>= 0.17
   ghc-options:         -threaded
 
 library

src/Chapter1.hs

@@ -71,6 +71,7 @@ Modules should have the same name as the corresponding file with
 the `.hs` extension.
 -}
 module Chapter1 where
+import Data.List
 
 {- |
 In Haskell, we have __expressions__. Expressions can be represented by some
@@ -209,31 +210,31 @@ 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 p => p
 
 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 +302,43 @@ 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
@@ -429,6 +430,7 @@ task is to specify the type of this function.
 49
 -}
 
+squareSum :: Int -> Int -> Int
 squareSum x y = (x + y) * (x + y)
 
 
@@ -449,7 +451,7 @@ 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
@@ -490,9 +492,8 @@ 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 = mod (abs n) 10
 {- |
 =⚔️= Task 6
 
@@ -520,7 +521,9 @@ 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
 
 
 {- |
@@ -554,7 +557,10 @@ 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 :: Integral a => a -> a -> a -> a
+mid x y z = (sort [x, y, z]) !! 1
 
 {- |
 =⚔️= Task 8
@@ -568,7 +574,15 @@ 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 
+  | otherwise = False 
+
 
 
 {- |
@@ -632,7 +646,16 @@ 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 :: Int -> Int
+-- sumLast2 n = let a = mod (abs n) 100
+--                  b = mod a 10
+--                  c = div a 10
+--               in 
+--                 c + b
+sumLast2 n = x + y 
+          where a = abs n
+                (_, b) = divMod a 100
+                (x, y) = divMod b 10
 
 
 {- |
@@ -653,7 +676,13 @@ 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 
+            | y < 10 = y
+            | x < 10 = x
+            | otherwise = firstDigit x
+            where y = abs n
+                  x = div y 10
 
 
 {-