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/Mem.hs | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 Haskell-book/15/semigroup/src/Mem.hs

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

diff --git a/Haskell-book/15/semigroup/src/Mem.hs b/Haskell-book/15/semigroup/src/Mem.hs
new file mode 100644
index 0000000..575e82d
--- /dev/null
+++ b/Haskell-book/15/semigroup/src/Mem.hs
@@ -0,0 +1,11 @@
+module Mem where
+
+newtype Mem s a =
+    Mem {
+        runMem :: s -> (a,s)
+    }
+
+instance Monoid a => Monoid (Mem s a) where
+    mempty = Mem $ \x -> (mempty, x)
+    mappend (Mem f1) (Mem f2) = Mem f
+        where f x = ((mappend (fst $ f1 x) (fst $ f2 x)), snd $ f2 $ snd $ f1 x)
-- 
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