From 871d3761cb1d12c593ad3a4aa059cc23ae35f87a Mon Sep 17 00:00:00 2001
From: Edoardo La Greca
Date: Mon, 7 Jul 2025 17:26:34 +0200
Subject: add third exercise of lecture 4

---
 lec04/hw.hs | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'lec04/hw.hs')

diff --git a/lec04/hw.hs b/lec04/hw.hs
index bb5a026..923ec01 100644
--- a/lec04/hw.hs
+++ b/lec04/hw.hs
@@ -37,3 +37,14 @@ treeInsertBalanced t@(Node h tl@(Node hl _ _ _) e tr@(Node hr _ _ _)) a
 
 foldTree :: [a] -> Tree a
 foldTree = foldr (flip treeInsertBalanced) Leaf
+
+-- Exercise 3
+
+xor :: [Bool] -> Bool
+xor = odd . foldl (\s x -> if x then s+1 else s) 0
+
+map' :: (a -> b) -> [a] -> [b]
+map' f = foldr (\x s -> f x : s) []
+
+myFoldl :: (a -> b -> a) -> a -> [b] -> a
+myFoldl f base xs = foldr (flip f) base (reverse xs)
-- 
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