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diff --git a/lec07/JoinList.hs b/lec07/JoinList.hs
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+module JoinList where
+
+data JoinList m a = Empty
+                  | Single m a
+                  | Append m (JoinList m a) (JoinList m a)
+  deriving (Eq, Show)
+
+-- Exercise 1
+
+tag :: Monoid m => JoinList m a -> m
+tag Empty = mempty
+tag Single m _ = m
+tag Append m _ _ = m
+
+(+++) :: Monoid m => JoinList m a -> JoinList m a -> JoinList m a
+(+++) jl1 jl2 = mappend jl1 jl2
+