1 files changed, 19 insertions, 0 deletions
diff --git a/Haskell-book/15/semigroup/src/Or.hs b/Haskell-book/15/semigroup/src/Or.hs
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+++ b/Haskell-book/15/semigroup/src/Or.hs
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+module Or where
+
+import Data.Semigroup
+import Test.QuickCheck
+
+data Or a b =
+    Fst a
+  | Snd b
+  deriving (Eq, Show)
+
+instance Semigroup (Or a b) where
+    (Snd x) <> _ = Snd x
+    _ <> x = x
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Or a b) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        frequency [ (1, return $ Fst x), (1, return $ Snd y) ]