From 878ca0a64f00d699c184dece89cc102b5e5f5169 Mon Sep 17 00:00:00 2001
From: cdamours <cdamours@arista.com>
Date: Fri, 26 Jun 2026 10:26:17 -0400
Subject: [PATCH] Stop greedy choice after full input match

A most-greedy Choice selects the valid alternative that advances furthest through the input. Once an alternative reaches the end of the input, no later alternative can produce a longer match.

This improves grammars with large Choice elements where an early alternative fully matches a complete statement. The parser can avoid walking the remaining alternatives while preserving most-greedy semantics.
---
 pyleri/choice.py    |  2 ++
 test/test_choice.py | 16 ++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/pyleri/choice.py b/pyleri/choice.py
index 9026fd9..3a6e8fe 100644
--- a/pyleri/choice.py
+++ b/pyleri/choice.py
@@ -37,6 +37,8 @@ def _most_greedy_result(self, root, tree, rule, s, node):
             if is_valid and pos > mg_pos:
                 node.children = children
                 mg_is_valid, mg_pos = is_valid, pos
+                if pos == root._len_string:
+                    break
 
         if mg_is_valid:
             root._append_tree(tree, node, mg_pos)
diff --git a/test/test_choice.py b/test/test_choice.py
index 105fc7b..4db8566 100644
--- a/test/test_choice.py
+++ b/test/test_choice.py
@@ -7,10 +7,12 @@
 from pyleri import (
     KeywordError,
     create_grammar,
+    Repeat,
     Sequence,
     Choice,
     Keyword,
     Regex,
+    Token,
 )  # nopep8
 
 
@@ -28,6 +30,20 @@ def test_choice_most_greedy(self):
         self.assertTrue(grammar.parse(' hi iris ').is_valid)
         self.assertFalse(grammar.parse(' hi sasha ').is_valid)
 
+    def test_choice_most_greedy_selects_full_match(self):
+        short = Token('a')
+        long = Token('aa')
+        grammar = create_grammar(Repeat(Choice(short, long)))
+
+        result = grammar.parse('aa')
+        repeat_node = result.tree.children[0]
+        choice_node = repeat_node.children[0]
+
+        self.assertTrue(result.is_valid)
+        self.assertEqual(len(repeat_node.children), 1)
+        self.assertEqual(choice_node.children[0].element, long)
+        self.assertEqual(choice_node.children[0].string, 'aa')
+
     def test_choice_first_match(self):
         k_hi = Keyword('hi')
         k_iris = Keyword('iris')