From 6a0d7f5c434c3564d0119befb6799fd77581050a Mon Sep 17 00:00:00 2001
From: Paul Oliver <contact@pauloliver.dev>
Date: Fri, 3 Jan 2025 11:01:20 -0800
Subject: Initial

---
 ch03_03-i.hs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 ch03_03-i.hs

(limited to 'ch03_03-i.hs')

diff --git a/ch03_03-i.hs b/ch03_03-i.hs
new file mode 100644
index 0000000..ec12e08
--- /dev/null
+++ b/ch03_03-i.hs
@@ -0,0 +1,25 @@
+-- Exercise 3-i
+-- Which of these types are `Functor`s? Give instances for the ones that are.
+
+-- `T1` is a `Functor`:
+newtype T1 a
+  = T1 (Int -> a)
+
+instance Functor T1 where
+  fmap f (T1 g) = T1 $ f <$> g
+
+newtype T2 a
+  = T2 (a -> Int)
+
+newtype T3 a
+  = T3 (a -> a)
+
+newtype T4 a
+  = T4 ((Int -> a) -> Int)
+
+-- `T5` is a `Functor`:
+newtype T5 a
+  = T5 ((a -> Int) -> Int)
+
+instance Functor T5 where
+  fmap f (T5 g) = T5 $ \f' -> g $ f' . f
-- 
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