Create a Covariant implementation

Exercises/exercise-5/Solution.hs

@@ -1,4 +1,7 @@
+import Data.Bits
 import Data.Char
+import Data.Functor.Contravariant
+
 data Result t =
     Result {
         actual :: t,
@@ -71,3 +74,51 @@ test22 = Result actual expected (actual == expected)
 -- >>> test22
 -- Result {actual = "HBC", expected = "HBC", result = True}
 --
+
+--------------------
+-- Exercise 3
+--------------------
+newtype ToInt b = ToInt {conv :: b -> Int}
+
+instance Contravariant ToInt where
+    contramap f (ToInt g) = ToInt (\ value -> g (f value))
+
+strHash :: String -> Int
+strHash value = realHash 0 value
+    where
+        realHash acc "" = acc
+        realHash acc (char:str) = realHash (acc + ((ord char) .&. 0b11010110)) str
+
+test3 = [
+        (Result strExpected strActual (strExpected == strActual)),
+        (Result expected actual (expected == actual))
+    ]
+    where
+        -- Create object `toInt` for converting strings to an Int hash (using the "strHash" function)
+        toInt = ToInt strHash
+
+        -- Converting a string to an Int hash using `toInt` should yield
+        -- the same result like using `strHash` directly
+        strActual = conv toInt myStr
+        strExpected = strHash myStr
+
+        -- Create a function for converting a `Char` to a `String`
+        charToStr = \x -> [x]
+
+        -- Wrap `toInt` in a (Char -> String) converter using `contramap`
+        -- effectively using `toInt` as a `Char -> Int` function
+        actual = conv (contramap charToStr toInt) myChar
+        -- should yield the same result like using `charToStr` and the original `toInt` directly
+        expected = conv toInt (charToStr myChar)
+
+        -- Value for testing the `toInt` implementation
+        myStr = "Hello World"
+        -- Value for testing the `toInt` implementation
+        -- wrapped in the `charToStr` function
+        myChar = 'V'
+
+-- Showing the result of the `String` and the `Char` test
+-- >>> mapM_ putStrLn (map show test3)
+-- Result {actual = 712, expected = 712, result = True}
+-- Result {actual = 86, expected = 86, result = True}
+--