Add remaining haskell book exercises

1 files changed, 17 insertions, 0 deletions

diff --git a/Haskell-book/15/semigroup/src/Validation.hs b/Haskell-book/15/semigroup/src/Validation.hs
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+++ b/Haskell-book/15/semigroup/src/Validation.hs
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+module Validation where
+
+import Data.Semigroup
+import Test.QuickCheck (arbitrary, Arbitrary(..), frequency)
+
+data Validation a b = Failure a | Success b deriving (Eq, Show)
+
+instance Semigroup a => Semigroup (Validation a b) where
+    (Success x) <> _ = Success x
+    _ <> (Success x) = Success x
+    (Failure x) <> (Failure y) = Failure $ x <> y
+
+instance (Arbitrary a, Arbitrary b) => Arbitrary (Validation a b) where
+    arbitrary = do
+        x <- arbitrary
+        y <- arbitrary
+        frequency [ (1, return $ Success x), (1, return $ Failure y) ]