5 ms·

The constraint is enforced at every move. Stockfish can never actually play against it. The only limitation is that its internal search tree imagines unconstrai

by vigrant 7mo ago

The constraint is enforced at every move. Stockfish can never actually play against it. The only limitation is that its internal search tree imagines unconstrained future moves, which makes its evaluation slightly off and the engine effectively weaker. For the use case (handicapping for fun) that's an acceptable tradeoff https://constrainedchess.vercel.app/?fen=2b1kb2%2F8%2F8%2F8%2F8%2F8%2FPPPPPPPP%2FRNBQKBNR+w+KQ+-+0+1&skill=10&c=engine%7CBishops+are+only+capable+of+moving+2+squares+maximum https://constrainedchess.vercel.app/?fen=2b1kb2%2F8%2F8%2F8%...

vunderba 7mo ago
> The only limitation is that its internal search tree imagines unconstrained future moves. Yes this is what I'm saying. Evaluation can be way more than just "slightly off" though and can make the evaluation MUCH weaker because it might go down "ply-routes" that aren't just suboptimal - they simply wouldn't work at all. For example thinking it had a "move set" that lead to a checkmate but the final ply involves a bishop that is five squares away per my rule constraint mentioned earlier. It's fine for fun but the statement that "Stockfish's skill level applies correctly" is not a true one at any moderate level of play. (above 1200 ELO). That's why I suggested looking into Fairy which supports runtime rule variations.
- vigrant 7mo ago
  Yup, you are right. I'll take a look at Fairy. Looks like there is a WASM version!
  - vunderba 7mo ago
    Nice, had no idea they'd ported it over to WASM. I've used the original Fairy to play Chinese chess in the past though and it worked great!
- vigrant 7mo ago
  So did some research.... Fairy would help with search tree accuracy but it's not expressive enough to cover everything, you can't encode "no captures for 5 moves" in an INI config. I'd still need the JS filtering layer for dynamic constraints, so you would end up in the same place with those cases.
  - vunderba 7mo ago
    Ah yeah that'll get complicated quickly. :( It'd be nice if stockfish or its variants exposed the "ply searcher" with some kind of a callback so you could quickly kill a ply based on your custom constraints. When I was doing some research into rolling my own chess engine about 5 years ago I stumbled across this: https://github.com/josefjadrny/js-chess-engine https://github.com/josefjadrny/js-chess-engine But you'd have to modify its minimax search and now we're getting pretty deep down the rabbit hole. Either way, good luck!

by vigrant 7mo ago

vunderba 7mo ago

> The only limitation is that its internal search tree imagines unconstrained future moves. Yes this is what I'm saying. Evaluation can be way more than just "slightly off" though and can make the evaluation MUCH weaker because it might go down "ply-routes" that aren't just suboptimal - they simply wouldn't work at all. For example thinking it had a "move set" that lead to a checkmate but the final ply involves a bishop that is five squares away per my rule constraint mentioned earlier. It's fine for fun but the statement that "Stockfish's skill level applies correctly" is not a true one at any moderate level of play. (above 1200 ELO). That's why I suggested looking into Fairy which supports runtime rule variations.

vigrant 7mo ago
Yup, you are right. I'll take a look at Fairy. Looks like there is a WASM version!
- vunderba 7mo ago
  Nice, had no idea they'd ported it over to WASM. I've used the original Fairy to play Chinese chess in the past though and it worked great!
vigrant 7mo ago
So did some research.... Fairy would help with search tree accuracy but it's not expressive enough to cover everything, you can't encode "no captures for 5 moves" in an INI config. I'd still need the JS filtering layer for dynamic constraints, so you would end up in the same place with those cases.
- vunderba 7mo ago
  Ah yeah that'll get complicated quickly. :( It'd be nice if stockfish or its variants exposed the "ply searcher" with some kind of a callback so you could quickly kill a ply based on your custom constraints. When I was doing some research into rolling my own chess engine about 5 years ago I stumbled across this: https://github.com/josefjadrny/js-chess-engine https://github.com/josefjadrny/js-chess-engine But you'd have to modify its minimax search and now we're getting pretty deep down the rabbit hole. Either way, good luck!