support ?

1 files changed, 13 insertions, 11 deletions

diff --git a/parsers.py b/parsers.py
index c851647..4924fbc 100644
--- a/parsers.py
+++ b/parsers.py
@@ -97,19 +97,21 @@ def _regex_to_ast(tokens):
     if '|' in tokens:
         i = tokens.index('|')
         return ('OR', _regex_to_ast(tokens[:i]), _regex_to_ast(tokens[i+1:]))
-    if tokens[-1] == '*':
-        if len(tokens) == 2:
-            return ('KLEENE', _regex_to_ast(tokens[:-1]))
-        else:
-            return ('CONCAT', _regex_to_ast(tokens[:-2]),
-                    ('KLEENE', _regex_to_ast(tokens[-2:-1])))
-    if tokens[-1] == '+':
+
+    if len(tokens) == 2 and tokens[-1] in ("*", "+", "?"):
         arg_ast = _regex_to_ast(tokens[:-1])
-        if len(tokens) == 2:
+        if tokens[-1] == '*':
+            return ('KLEENE', arg_ast)
+        elif tokens[-1] == '+':
             return ('CONCAT', arg_ast, ('KLEENE', arg_ast))
+        elif tokens[-1] == "?":
+            return ('OR', _regex_to_ast([EPSILON]), arg_ast)
         else:
-            return ('CONCAT', _regex_to_ast(tokens[:-2]),
-                    ('CONCAT', arg_ast, ('KLEENE', _regex_to_ast(tokens[-2:-1]))))
+            print(tokens)
+            raise NotImplementedError
+
+    if tokens[-1] in ("*", "?", "+"):
+        return ('CONCAT', _regex_to_ast(tokens[:-2]), _regex_to_ast(tokens[-2:]))
     return ('CONCAT', _regex_to_ast(tokens[:-1]), _regex_to_ast(tokens[-1:]))
 
 def match_parens(tokens):
@@ -131,7 +133,7 @@ def lex_regex(string):
     while string:
         if string[0].isspace():
             string = string[1:]
-        elif string[0] in ("(", ")", "|", "*", "+") + ALPHABET:
+        elif string[0] in ("(", ")", "|", "*", "+", "?") + ALPHABET:
             tokens.append(string[0])
             string = string[1:]
         elif string[0] == "E":