From 98329e0a3dd4f78b5d815ac3896272ec70904901 Mon Sep 17 00:00:00 2001
From: Eugen Wissner <belka@caraus.de>
Date: Thu, 11 Dec 2025 10:28:11 +0100
Subject: Add remaining haskell book exercises

---
 Haskell-book/15/semigroup/src/Combine.hs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 Haskell-book/15/semigroup/src/Combine.hs

(limited to 'Haskell-book/15/semigroup/src/Combine.hs')

diff --git a/Haskell-book/15/semigroup/src/Combine.hs b/Haskell-book/15/semigroup/src/Combine.hs
new file mode 100644
index 0000000..fe420dd
--- /dev/null
+++ b/Haskell-book/15/semigroup/src/Combine.hs
@@ -0,0 +1,25 @@
+{-# LANGUAGE FlexibleInstances #-}
+module Combine where
+
+import Data.Semigroup
+import Test.QuickCheck
+
+newtype Combine a b =
+    Combine { unCombine :: (a -> b) }
+
+instance Semigroup b => Semigroup (Combine a b) where
+    (Combine f1) <> (Combine f2) = Combine f
+        where f x = (f1 x) <> (f2 x)
+
+instance (Monoid b) => Monoid (Combine a b) where
+    mempty = Combine $ \_ -> mempty
+    mappend (Combine f1) (Combine f2) = Combine f
+        where f x = mappend (f1 x) (f2 x)
+
+instance (Num a, CoArbitrary a, Arbitrary b) => Arbitrary (Combine a b) where
+    arbitrary = do
+        f <- arbitrary
+        return $ Combine (\n -> f n)
+
+instance (Show a, Show b) => Show (Combine a b) where
+    show _ = "a -> b"
-- 
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