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

---
 ch10_10.2-i.hs | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 ch10_10.2-i.hs

(limited to 'ch10_10.2-i.hs')

diff --git a/ch10_10.2-i.hs b/ch10_10.2-i.hs
new file mode 100644
index 0000000..a8f1d20
--- /dev/null
+++ b/ch10_10.2-i.hs
@@ -0,0 +1,17 @@
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE TypeFamilies #-}
+
+-- Exercise 10.2-i
+-- Defunctionalize `listToMaybe` at the type-level.
+
+import Data.Kind (Type)
+
+type Exp a = a -> Type
+
+type family Eval (e :: Exp a) :: a
+
+data ListToMaybe :: [a] -> Exp (Maybe a)
+
+type instance Eval (ListToMaybe '[]) = 'Nothing
+
+type instance Eval (ListToMaybe (x ': _)) = 'Just x
-- 
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