implement defparser macro

[judepayne]

Hi, I was thinking about the defparser macro. Of course it couldn't possibly have worked inside the pod as it's defining a var in a different process :)
However, we should be able to implement it in instaparse-bb, perhaps starting with a simple version then moving to one which splits the work appropriately between compile time and runtime as instaparse itself does.

Possibly we could go further and have Parser as a record that implements Ifn (like instaparse) and so remove the limitation that parsers must be called with parse.
@borkdude you must have considered this when you implemented the instaparse pod and instaparse-bb, so it would be good to hear your thoughts.

[borkdude]

My thoughts: I just haven't thought deeply about it yet :)

[judepayne]

Lol. I'll investigate more deeply. Knock some code together as time permits. I think it's possible. You'd just have to port or re-implement most of the instaparse.core ns (which is not that big).

[judepayne]

Removing the limitation that parsers must be called with parse will be hard without support for implementing IFn on records or types.

A simple defparser macro to get us closer to the instaparse interface is straightforward enough. I'll do a PR

[judepayne]

Closing.
instaparse-bb updated with:

• the defparser macro
• Parsers can be called directly like they're fns, as per Instaparse. Although currently in babashka, you can't have Records implement IFn, this can be worked around by using reify instead.