From f46dafc461e4ee3fa1637051284f89b443f00a51 Mon Sep 17 00:00:00 2001
From: Edoardo La Greca
Date: Tue, 9 Sep 2025 20:38:00 +0200
Subject: add files for lecture 7's homework

---
 lec07/Sized.hs | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 lec07/Sized.hs

(limited to 'lec07/Sized.hs')

diff --git a/lec07/Sized.hs b/lec07/Sized.hs
new file mode 100644
index 0000000..9214b76
--- /dev/null
+++ b/lec07/Sized.hs
@@ -0,0 +1,28 @@
+{-# LANGUAGE GeneralizedNewtypeDeriving, FlexibleInstances #-}
+module Sized where
+
+import Data.Monoid
+
+newtype Size = Size Int
+  deriving (Eq, Ord, Show, Num)
+
+getSize :: Size -> Int
+getSize (Size i) = i
+
+class Sized a where
+  size :: a -> Size
+
+instance Sized Size where
+  size = id
+
+-- This instance means that things like
+--   (Foo, Size)
+--   (Foo, (Bar, Size))
+--   ...
+-- are all instances of Sized.
+instance Sized b => Sized (a,b) where
+  size = size . snd
+
+instance Monoid Size where
+  mempty  = Size 0
+  mappend = (+)
-- 
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