Standalone parser cannot be used more than once

That is, Lark_StandAlone().parse() cannot be called more than once on different inputs. This is from master. I found two reasons for it:

• rule.alias is overwritten permanently in ParseTreeBuilder.create_callback(), causing errors elsewhere on subsequent runs.
• In Python 3, the wrapper_chain = filter(...) in ParseTreeBuilder._init_builders() creates a filter object that can only be consumed once.

Now, within an already-generated standalone parser, I’ve found it suffices to make the following edits:

• Rule.__init__(): add self.cb_name = None
• Line 2 of Lark_StandAlone.__init__(): change to callbacks = {rule: getattr(callback, rule.cb_name or rule.origin, None) for rule in RULES.values()}
• Line 19 of ParseTreeBuilder.create_callback(): change to rule.cb_name = internal_callback_name
• Line 6 of ParseTreeBuilder._init_builders(): change to wrapper_chain = list(filter(None, [

However, when trying to edit these into Lark itself (so that lark.tools.standalone would create a parser file with these changes already in place), the addition of the Rule().cb_name attribute caused lots of errors/failed tests – and I couldn’t be positive where in the package to replace rule.alias and where not to. So I’m pretty sure it’s not the way to go. Thoughts?

[erezsh]

Should work now on master.

[erezsh]

Thanks for the bug report. I know what’s the problem, and I plan to fix it soon.