[ ] Be able to localize syntax errors in sublanguages. Status quo: If the subscanner produces a bad expression, error localization fails because it can't unparse.
[ ] Fail gracefully if a subscanner or subparser crashes. Status quo: If the wrapped subscanner throws an exception, it gets raised in the wrong thread and hangs Python.
However, annotation of post-parsing errors seems to work, because the offending syntax is unparsed into the equivalent ChurchPrime anyway!
However, annotation of post-parsing errors seems to work, because the offending syntax is unparsed into the equivalent ChurchPrime anyway!