Lark: How to handle empty input?

[jnikula]

I've got a small query language where the empty string makes sense as a query. I'm handling it as a special case outside of Lark, and I'd like to be able to get rid of that special case. I've tried things like:

?start: the_actual_grammar
| "" -> op_empty

and:

?start: the_actual_grammar
| / */ -> op_empty

But it fails with "Dynamic Earley doesn't allow zero-width regexps" which pretty much explains the situation.

Any ideas how to work around this?

[erezsh]

Why not use an empty rule?

>>> p = Lark('!start: "a" | ')
>>> p.parse('a')
Tree(start, [Token(A, 'a')])
>>> p.parse('')
Tree(start, [])

[jnikula]

Thanks, didn't realize that was possible!