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