From e2f3c264f333152a28434c4d5a4a2dd3534581c9 Mon Sep 17 00:00:00 2001
From: BrandonPacewic <92102436+BrandonPacewic@users.noreply.github.com>
Date: Tue, 27 Jan 2026 00:35:19 -0800
Subject: [PATCH 1/2] test: added `y_combinator` test

---
 tests/cpl/y_combinator/test.cpp | 72 +++++++++++++++++++++++++++++++++
 1 file changed, 72 insertions(+)
 create mode 100644 tests/cpl/y_combinator/test.cpp

diff --git a/tests/cpl/y_combinator/test.cpp b/tests/cpl/y_combinator/test.cpp
new file mode 100644
index 0000000..0fc35f6
--- /dev/null
+++ b/tests/cpl/y_combinator/test.cpp
@@ -0,0 +1,72 @@
+// Copyright (c) Brandon Pacewic
+// SPDX-License-Identifier: MIT
+
+#include <cassert>
+#include <vector>
+
+#include "xutility.h"
+
+int main() {
+    using namespace cpl;
+    {
+        auto factorial = y_combinator([](auto self, int n) -> int {
+            return n <= 1 ? 1 : n * self(n - 1);
+        });
+
+        assert(factorial(0) == 1);
+        assert(factorial(1) == 1);
+        assert(factorial(5) == 120);
+        assert(factorial(10) == 3628800);
+    }
+    {
+        auto gcd = y_combinator([](auto self, int a, int b) -> int {
+            return b == 0 ? a : self(b, a % b);
+        });
+
+        assert(gcd(20, 30) == 10);
+        assert(gcd(48, 18) == 6);
+        assert(gcd(0, 5) == 5);
+        assert(gcd(17, 13) == 1);
+    }
+    {
+        auto fib = y_combinator([](auto self, int n) -> int {
+            return n <= 1 ? n : self(n - 1) + self(n - 2);
+        });
+
+        assert(fib(0) == 0);
+        assert(fib(1) == 1);
+        assert(fib(10) == 55);
+        assert(fib(15) == 610);
+    }
+    {
+        std::vector<std::vector<int>> adj = {{1, 2}, {3, 4}, {}, {}, {}};
+        std::vector<int> visited;
+
+        auto dfs = y_combinator([&](auto self, int node) -> void {
+            visited.push_back(node);
+            for (int next : adj[node]) {
+                self(next);
+            }
+        });
+
+        dfs(0);
+        assert(visited.size() == 5);
+        assert(visited[0] == 0);
+        assert(visited[1] == 1);
+        assert(visited[2] == 3);
+        assert(visited[3] == 4);
+        assert(visited[4] == 2);
+    }
+    {
+        int call_count = 0;
+        auto counter = y_combinator([&](auto self, int n) -> int {
+            ++call_count;
+            return n <= 0 ? 0 : self(n - 1);
+        });
+
+        counter(5);
+        assert(call_count == 6);
+    }
+
+    return 0;
+}

From ac8c30fecfbec70edaad9b4b4411b8be9c539d62 Mon Sep 17 00:00:00 2001
From: BrandonPacewic <92102436+BrandonPacewic@users.noreply.github.com>
Date: Tue, 27 Jan 2026 00:35:58 -0800
Subject: [PATCH 2/2] fix: formatting

---
 tests/cpl/y_combinator/test.cpp | 18 ++++++------------
 1 file changed, 6 insertions(+), 12 deletions(-)

diff --git a/tests/cpl/y_combinator/test.cpp b/tests/cpl/y_combinator/test.cpp
index 0fc35f6..5092e73 100644
--- a/tests/cpl/y_combinator/test.cpp
+++ b/tests/cpl/y_combinator/test.cpp
@@ -9,9 +9,7 @@
 int main() {
     using namespace cpl;
     {
-        auto factorial = y_combinator([](auto self, int n) -> int {
-            return n <= 1 ? 1 : n * self(n - 1);
-        });
+        auto factorial = y_combinator([](auto self, int n) -> int { return n <= 1 ? 1 : n * self(n - 1); });
 
         assert(factorial(0) == 1);
         assert(factorial(1) == 1);
@@ -19,9 +17,7 @@ int main() {
         assert(factorial(10) == 3628800);
     }
     {
-        auto gcd = y_combinator([](auto self, int a, int b) -> int {
-            return b == 0 ? a : self(b, a % b);
-        });
+        auto gcd = y_combinator([](auto self, int a, int b) -> int { return b == 0 ? a : self(b, a % b); });
 
         assert(gcd(20, 30) == 10);
         assert(gcd(48, 18) == 6);
@@ -29,9 +25,7 @@ int main() {
         assert(gcd(17, 13) == 1);
     }
     {
-        auto fib = y_combinator([](auto self, int n) -> int {
-            return n <= 1 ? n : self(n - 1) + self(n - 2);
-        });
+        auto fib = y_combinator([](auto self, int n) -> int { return n <= 1 ? n : self(n - 1) + self(n - 2); });
 
         assert(fib(0) == 0);
         assert(fib(1) == 1);
@@ -40,7 +34,7 @@ int main() {
     }
     {
         std::vector<std::vector<int>> adj = {{1, 2}, {3, 4}, {}, {}, {}};
-        std::vector<int> visited;
+        std::vector<int>              visited;
 
         auto dfs = y_combinator([&](auto self, int node) -> void {
             visited.push_back(node);
@@ -58,8 +52,8 @@ int main() {
         assert(visited[4] == 2);
     }
     {
-        int call_count = 0;
-        auto counter = y_combinator([&](auto self, int n) -> int {
+        int  call_count = 0;
+        auto counter    = y_combinator([&](auto self, int n) -> int {
             ++call_count;
             return n <= 0 ? 0 : self(n - 1);
         });