Add remaining haskell book exercises

Haskell-book/14/addition/Addition.hs

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+module Addition where
+
+import Test.Hspec
+import Test.QuickCheck
+
+dividedBy :: Integral a => a -> a -> (a, a)
+dividedBy num denom = go num denom 0
+    where go n d count
+            | n < d = (count, n)
+            | otherwise =  go (n - d) d (count + 1)
+
+multiplyBy :: (Ord a, Eq a, Num a) => a -> a -> a
+multiplyBy a b
+    | a == 0 || b == 0 = 0
+    | a > 0 && b > 0   = multiplyBy' a b
+    | a < 0 && b < 0   = multiplyBy' (-a) (-b)
+    | a < 0 && b > 0   = -(multiplyBy' (-a) b)
+    | a > 0 && b < 0   = -(multiplyBy' a (-b))
+    where  multiplyBy' c 1 = c
+           multiplyBy' c d = c + (multiplyBy c (d - 1))
+
+main :: IO ()
+main = hspec $ do
+    describe "Addition" $ do
+        it "15 divided by 3 is 5" $ do
+            dividedBy 15 3 `shouldBe` (5, 0)
+        it "22 divided by 5 is 4 remainder 2" $ do
+            dividedBy 22 5 `shouldBe` (4, 2)
+        it "x + 1 is always greater than x" $ do
+            property $ \x -> x + 1 > (x :: Int)
+    describe "Multiplication" $ do
+        it "15 multiplied by 3 is 45" $ do
+            multiplyBy 15 3 `shouldBe` 45
+        it "22 multiplied by 5 is 110" $ do
+            multiplyBy 22 5 `shouldBe` 110