For people who are interested, here is the solution. In standard PGN, the solution is:

1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nxe4 4. Qe2 Nxd2 5. Nc6+ Ne4 6. Nxd8 Kxd8 7. Qxe4 a6 8. Bg5+ Be7 9. Qxe7#

In the Stockfish notation this engine uses, White’s moves are:

1. e2e4 2. g1f3 3. f3e5 4. d1e2 5. e5c6 6. c6d8 7. e2e4 8. c1g5 9. e4e7

Here is a Lichess analysis of this game:

https://lichess.org/WnMF3LpX

(In terms of Regexes, Javascript has a very rich Turing complete Regex library; it’s an open question whether Lua 5.1’s regexes are Turing complete, but they are good enough for the text processing I do)

This is amazing. I'm at loss for words.

During my CS years I remember being fascinated by NFA's, as opposed to boring single universe DFA's.

For some reason I internalized that I would never see something like an NFA implemented beyond text books.

Then came Carlini.

• bigdict

  today at 3:59 AM

  But... they are equivalent?

  • xpon

    today at 4:49 AM

    Modulo an exponential blowup! That’s like saying P is equivalent to NP.

Upon reading the title, this is one of those "I know that's possible, but I'd never bother to implement it" things, although this particular implementation isn't exactly what I had in mind.

The technical write up is worth perusing but I played a game before reading and accidentally found a winning strategy immediately. I'm not sure if this is a result of the 2-ply nature of the engine or if the mentioned deficiencies account for this but the computer did not act to prevent checkmate in 1 (without any intervening check); the game I played was (in algebraic notation): 1. e4 e5 2. kf3 kf6 3. kxe5 kxe4 4. d4 kxf2 5. Kxf2 a5 6. Qf3 b5?? 7. Qxf7 1-0

And now you have 84,689 problems

I get "illegal move, game over" like 50% of the time, chrome on android.

This is like a fever dream.

This is absurd. I did not realize you could do nearly this much computation in regex.

• karlgkk

  today at 4:37 AM

  It’s turing complete so you could compile almost any language to regex. You might have to build a vm for some languages, also in regex. The point is, it’s regex all the way down.

2025