TODO.md

Current Internal Structure

Internal state mostly consists of:

[{
    type: 'term',
    term: 'a'
}, {
    type: 'term', // notice how a repeat doesn't change the type?
    term: '(?:abc)*'
}, {
    type: 'open_or',
    term: 'ab|cd'
}, {
    type: 'term',
    captures: ['inner-before-1', 'inner-before-2']
    term: '(abc)(def)'
}, {
    type: 'term', // still no type changes through all these ops...
    captures: ['outer-with-star', 'inner-1', 'inner-2']
    term: '((?:(abc)(def))*)'
}]

On the backlog: A backref node would just look something like {type: 'term', backrefs: ['outer-with-star']}. Better than the alternative of storing it as a plain string and having to postprocess the thing or something.

Scratchpad

A little too unrealistic, above. Having fancy backrefs like that almost seems nice, until I consider: how would I process a .repeat() after the following?

seq( 'abc'.capture('g1'), backref('g1'), 'def' ) [{ term: ['(abc)', {backref: 'g1'}, 'def'] }]

Ultimately, string concatentation / modification is nice enough here, don't want to lose that. Instead:

[{ term: '(abc)\1def', captures: ['g1'] }]

And then, if someone says .capture('g2') after that:

[{ term: '((abc)\2def)', captures: ['g2', 'g1'] }]

The only time I think that processing backrefs in this way could cause "harm" is if it was in a char set, like /[\1]/, but that's already a meaningless regex, so no harm no foul.

Of course, can't blindly increment either. If \1 referenced a capture group from an earlier term, that wouldn't get updated.

Perhaps it would be simplest to keep some _captureIdx state, and have the burden on updating that go to the few methods that would update it, like closing groups and adding captures on terms that already have captures.

For above examples, fuller testcase would generate terms like:

[{ term: '(g1)', ... }, { term: '((abc)\1\3def)', captures: ['g2', 'g3'] }]

Including one backref to a thing just earlier in the seq, and one from before the seq.

PS, future me: it's turtles all the way down. What if someone wants to use the alternate API form with a seq naming a backref that doesn't exist yet?