From dc7e0fc6bd3a9542306f6271b9793a2969f79e22 Mon Sep 17 00:00:00 2001
From: lou lecrivain <lou.lecrivain@wdz.de>
Date: Mon, 23 Feb 2026 16:39:41 +0100
Subject: [PATCH] update typing of common "head()" function to reflect None
 return

makes typing issues throughout the source code visible to mypy
whereas they previously weren't
---
 cosmo/common.py | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/cosmo/common.py b/cosmo/common.py
index c5a164a..77fed47 100644
--- a/cosmo/common.py
+++ b/cosmo/common.py
@@ -53,8 +53,10 @@ def strictly_decreasing(l: Sequence[Comparable]) -> bool:
 
 
 # next() can raise StopIteration, so that's why I use this function
-# FIXME: should be head[T](l: list[T]) -> Optional[T]
-def head(l):
+T = TypeVar("T")
+
+
+def head(l: list[T]) -> Optional[T]:
     return None if not l else l[0]