From 1d91eb52b619c15d0ae927730e464616a08137f2 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Mon, 22 Nov 2021 06:00:05 +0000
Subject: (list)+reduce function

Basically accumulates values, check
https://en.wikipedia.org/wiki/Fold_(higher-order_function) for more
detail.
---
 list.cpp | 13 +++++++++++++
 1 file changed, 13 insertions(+)

(limited to 'list.cpp')

diff --git a/list.cpp b/list.cpp
index e95a0ac..b83b018 100644
--- a/list.cpp
+++ b/list.cpp
@@ -63,6 +63,18 @@ void map(List<T> *lst, U (*f)(T))
   map(lst->next, f);
 }
 
+template <typename T>
+T reduce(List<T> *lst, T (*reducer) (T, T), T init = 0)
+{
+  if (!lst)
+    return init;
+  if (!init)
+    init = lst->value;
+  else
+    init = reducer(init, lst->value);
+  return reduce(lst->next, reducer, init);
+}
+
 template <typename T>
 std::ostream& operator<<(std::ostream& ostream, const List<T> *lst)
 {
@@ -82,6 +94,7 @@ int main(void)
   std::cout << lst << std::endl;
   map<int, int>(lst = reverse(lst), [](int x){ return x * 2; });
   std::cout << lst << std::endl;
+  std::cout << reduce<int>(lst, [](int a, int b) { return a + b; }, 0) << std::endl;
   delete lst;
   return 0;
 }
-- 
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