change Sized module due to old age

1 files changed, 13 insertions, 0 deletions

diff --git a/lec07/Sized.hs b/lec07/Sized.hs
index 9214b76..762d8fb 100644
--- a/lec07/Sized.hs
+++ b/lec07/Sized.hs
@@ -23,6 +23,19 @@ instance Sized Size where
 instance Sized b => Sized (a,b) where
   size = size . snd
 
+-- Since (<>) has been moved from Monoid to Semigroup, this little change is required
+
+-- Old version
+{-
 instance Monoid Size where
   mempty  = Size 0
   mappend = (+)
+-}
+
+-- New version
+instance Monoid Size where
+  mempty = Size 0
+
+instance Semigroup Size where
+  (<>) = (+)
+