diff --git a/lark/parsers/grammar_analysis.py b/lark/parsers/grammar_analysis.py
index 5cbd697..f34d5c1 100644
--- a/lark/parsers/grammar_analysis.py
+++ b/lark/parsers/grammar_analysis.py
@@ -136,7 +136,8 @@ class GrammarAnalyzer(object):
                     if not is_terminal(new_r):
                         yield new_r
 
-        _ = list(bfs([rule], _expand_rule))
+        for _ in bfs([rule], _expand_rule):
+            pass
 
         return fzset(init_ptrs)