Added test for recursive templates + implemented them

lark/load_grammar.py

@@ -384,6 +384,7 @@ class ApplyTemplates(Transformer_InPlace):
         args = c[1:]
         result_name = self._get_template_name(name.value, args)
         if result_name not in self.created_templates:
+            self.created_templates.add(result_name)
             (_n, params, tree, options) ,= (t for t in self.temp_defs if t[0] == name)
             assert len(params) == len(args), args
             result_tree = deepcopy(tree)

tests/test_parser.py

@@ -822,7 +822,18 @@ def _make_parser_test(LEXER, PARSER):
             self.assertSequenceEqual(x.children,['1', '2', '3', '4'])
             x = g.parse("[1]")
             self.assertSequenceEqual(x.children,['1'])
-            print(x)
+
+        def test_templates_recursion(self):
+            g = _Lark(r"""
+                       start: "[" sep{NUMBER, ","} "]"
+                       sep{item, delim}: item | sep{item, delim} delim item
+                       NUMBER: /\d+/
+                       %ignore " "
+                       """)
+            x = g.parse("[1, 2, 3, 4]")
+            self.assertSequenceEqual(x.children,['1', '2', '3', '4'])
+            x = g.parse("[1]")
+            self.assertSequenceEqual(x.children,['1'])
 
         def test_token_collision_WS(self):
             g = _Lark(r"""start: "Hello" NAME