chapter 15 - added exercise 11 for semigroups

Author: mukeshsoni

chapter15/exercises/semigroup/11_validation.hs

@@ -0,0 +1,27 @@
+import Test.QuickCheck
+import Data.Semigroup
+import SemigroupLaws
+
+data Validation a b =
+    Failure' a | Success' b
+    deriving (Eq, Show)
+
+instance Semigroup a =>
+    Semigroup (Validation a b) where
+        (Success' a) <> (Success' b) = Success' b
+        (Failure' a) <> (Failure' b) = Failure' (a <> b)
+        (Failure' a) <> (Success' b) = Failure' a
+        (Success' a) <> (Failure' b) = Failure' b
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Validation a b) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        oneof [return (Success' x), return (Failure' y)]
+
+type ValidationAssoc = Validation String String -> Validation String String -> Validation String String -> Bool
+type ValidationAssoc2 = Validation String Integer -> Validation String Integer -> Validation String Integer -> Bool
+
+main = do
+    quickCheck (assocLaw :: ValidationAssoc)
+    quickCheck (assocLaw :: ValidationAssoc2)

chapter15/exercises/semigroup/9_combine.hs

@@ -0,0 +1,10 @@
+-- TODO - couldn't figure out this exercise
+import Test.QuickCheck
+import Data.Semigroup
+import SemigroupLaws
+
+newtype Combine a b =
+    Combine {unCombine :: a -> b}
+
+instance Semigroup b => Semigroup (Combine a b) where
+    (Combine f) <> (Combine g) = Combine (f <> g)