From d587e3351a5d93b6463f58ec5bab1fd16c11b7a9 Mon Sep 17 00:00:00 2001
From: Eric Wolf <robo-eric@gmx.de>
Date: Tue, 4 Oct 2022 18:21:00 +0200
Subject: [PATCH] mark DepthFirstVisitor as final and add slots

---
 lambda_calculus/visitors/walking.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lambda_calculus/visitors/walking.py b/lambda_calculus/visitors/walking.py
index ac99738..90d164d 100644
--- a/lambda_calculus/visitors/walking.py
+++ b/lambda_calculus/visitors/walking.py
@@ -4,7 +4,7 @@
 
 from __future__ import annotations
 from collections.abc import Iterator
-from typing import TypeVar
+from typing import TypeVar, final
 from .. import terms
 from . import BottomUpVisitor
 
@@ -15,6 +15,7 @@
 V = TypeVar("V")
 
 
+@final
 class DepthFirstVisitor(BottomUpVisitor[Iterator["terms.Term[V]"], V]):
     """
     Visitor yielding subterms depth first
@@ -24,6 +25,8 @@ class DepthFirstVisitor(BottomUpVisitor[Iterator["terms.Term[V]"], V]):
         V: represents the type of variables used in terms
     """
 
+    __slots__ = ()
+
     def visit_variable(self, variable: terms.Variable[V]) -> Iterator[terms.Term[V]]:
         """
         Visit a Variable term.