From 46aab39ee6eb8c9fa0b774ce42b3f4bd6e63ab3d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Juhani=20Krekel=C3=A4?= <juhani@krekelä.fi>
Date: Fri, 31 May 2019 14:15:28 +0300
Subject: [PATCH] Remove empty literals when concatenating regexes

---
 regex.py | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/regex.py b/regex.py
index 3baf5f5..f0d4156 100644
--- a/regex.py
+++ b/regex.py
@@ -81,7 +81,11 @@ def concat(*elements):
 
 	combined = []
 	for element in flattened:
-		if len(combined) > 0 and type(combined[-1]) == Literal and type(element) == Literal:
+		if type(element) == Literal and element.text == '':
+			# Drop empty literals
+			continue
+
+		elif len(combined) > 0 and type(combined[-1]) == Literal and type(element) == Literal:
 			# Combine two literals next to each other
 			# into one literal
 			previous = combined.pop()
@@ -90,7 +94,11 @@ def concat(*elements):
 		else:
 			combined.append(element)
 
-	if len(combined) == 1:
+	if len(combined) == 0:
+		# Empty regex, represent with empty literal
+		return lit('')
+
+	elif len(combined) == 1:
 		element, = combined
 		return element
 	else: