From d029a171c0989eed302aaed871f68d41b641643a Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Tue, 28 Jan 2025 15:51:48 -0500
Subject: [PATCH] Changed behavior of SOS and EOS assertions depending on
 whether multiline mode is enabled or not

---
 nfa.go | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/nfa.go b/nfa.go
index a2ac5f0..bec935d 100644
--- a/nfa.go
+++ b/nfa.go
@@ -108,11 +108,15 @@ func (s State) checkAssertion(str []rune, idx int) bool {
 		return true
 	}
 	if s.assert == SOS {
-		return idx == 0
+		// Single-line mode: Beginning of string
+		// Multi-line mode: Previous character was newline
+		return idx == 0 || (multilineMode && (idx > 0 && str[idx-1] == '\n'))
 	}
 	if s.assert == EOS {
+		// Single-line mode: End of string
+		// Multi-line mode: current character is newline
 		// Index is at the end of the string, or it points to the last character which is a newline
-		return idx == len(str) || (idx == len(str)-1 && str[len(str)-1] == '\n')
+		return idx == len(str) || (multilineMode && str[idx] == '\n')
 	}
 	if s.assert == WBOUND {
 		return isWordBoundary(str, idx)