# HG changeset patch
# User Laman
# Date 2024-06-20 13:49:15
# Node ID 68c16b6d84f39bf6f5ea3b3be16ccc5037abf813
# Parent  e9496b21cf64964a03ba21a77aa7f051be0c683d

added the lambda transition

diff --git a/regexp.py b/regexp.py
--- a/regexp.py
+++ b/regexp.py
@@ -21,6 +21,19 @@ class Token:
 		pass
 
 
+class Lambda(Token):
+	is_skippable = True
+
+	def list_first(self):
+		yield from []
+
+	def list_last(self):
+		yield from []
+
+	def list_neighbours(self):
+		yield from []
+
+
 class Symbol(Token):
 	def __init__(self, position, value):
 		self.position = position
@@ -188,6 +201,9 @@ def parse(pattern, offset=0):
 			is_alternative = True
 			res.append(AlternativeSeparator())
 			i += 1
+		elif c == "_":
+			res.append(Lambda())
+			i += 1
 		else:
 			res.append(Symbol(i+offset, c))
 			i += 1
diff --git a/src/regexp/token.rs b/src/regexp/token.rs
--- a/src/regexp/token.rs
+++ b/src/regexp/token.rs
@@ -52,6 +52,7 @@ pub struct Chain {
 }
 
 pub enum Token {
+	Lambda,
 	Symbol(Symbol),
 	Asterisk(Asterisk),
 	Plus(Plus),
@@ -225,6 +226,7 @@ impl Chain {
 impl Token {
 	pub fn is_skippable(&self) -> bool {
 		match self {
+			Token::Lambda => true,
 			Token::Symbol(_) => false,
 			Token::Asterisk(_) => true,
 			Token::Plus(_) => false,
@@ -236,6 +238,7 @@ impl Token {
 
 	pub fn list_first(&self) -> Vec<usize> {
 		match self {
+			Token::Lambda => vec![],
 			Token::Symbol(t) => t.list_first(),
 			Token::Asterisk(t) => t.list_first(),
 			Token::Plus(t) => t.list_first(),
@@ -247,6 +250,7 @@ impl Token {
 
 	pub fn list_last(&self) -> Vec<usize> {
 		match self {
+			Token::Lambda => vec![],
 			Token::Symbol(t) => t.list_last(),
 			Token::Asterisk(t) => t.list_last(),
 			Token::Plus(t) => t.list_last(),
@@ -258,6 +262,7 @@ impl Token {
 
 	pub fn list_neighbours(&self) -> Vec<(usize, usize)> {
 		match self {
+			Token::Lambda => vec![],
 			Token::Symbol(t) => t.list_neighbours(),
 			Token::Asterisk(t) => t.list_neighbours(),
 			Token::Plus(t) => t.list_neighbours(),
@@ -313,6 +318,10 @@ pub fn parse(pattern: &String, offset: u
 				res.push(Box::new(Token::AlternativeSeparator));
 				i += 1;
 			}
+			'_' => {
+				res.push(Box::new(Token::Lambda));
+				i += 1;
+			}
 			_c => {
 				res.push(Box::new(Token::Symbol(Symbol{position: i+offset})));
 				i += 1;
diff --git a/tests/test_regexp.rs b/tests/test_regexp.rs
--- a/tests/test_regexp.rs
+++ b/tests/test_regexp.rs
@@ -89,6 +89,32 @@ fn test_eval_alternative_dfa() {
 }
 
 #[test]
+fn test_eval_lambda_nfa() {
+	let r = Regexp::new(&String::from("a_")).unwrap();
+	assert!(r.eval(String::from("a")));
+	assert!(!r.eval(String::from("")));
+	assert!(!r.eval(String::from("ab")));
+
+	let r = Regexp::new(&String::from("a|_")).unwrap();
+	assert!(r.eval(String::from("a")));
+	assert!(r.eval(String::from("")));
+	assert!(!r.eval(String::from("b")));
+}
+
+#[test]
+fn test_eval_lambda_dfa() {
+	let r = Regexp::new(&String::from("a_")).unwrap().determinize();
+	assert!(r.eval(String::from("a")));
+	assert!(!r.eval(String::from("")));
+	assert!(!r.eval(String::from("ab")));
+
+	let r = Regexp::new(&String::from("a|_")).unwrap().determinize();
+	assert!(r.eval(String::from("a")));
+	assert!(r.eval(String::from("")));
+	assert!(!r.eval(String::from("b")));
+}
+
+#[test]
 fn test_invalid_asterisk() {
 	let x = Regexp::new(&String::from("*"));
 	assert!(matches!(x, Err(ParsingError::Asterisk{s: _, pos: 0})));