Claude
284f9f3f95
The four games that were listed but not written. Nothing in the catalogue is marked "coming soon" any more. Checkers is English draughts on the thirty-two dark squares, numbered the way the game is written down. Captures are compulsory and a multiple jump is one move object, so a player cannot stop halfway through one — true by construction rather than by a rule that has to be enforced somewhere. The move generator matches the published perft counts at one to four ply (7, 49, 302, 1469), which fold in compulsory capture, crowning and the men's forward-only rule all at once. Backgammon's hard rule is not how a checker moves but that a player must use as much of the roll as they can, and that cannot be checked one move at a time: a move can be illegal precisely because playing it strands the other die. So the generator works backwards from whole turns — memoised depth-first over the remaining dice — and offers only the first steps of the longest plays. Recomputing it after each checker is what makes the rule true by construction. Every die comes from the table's seed and a count of rolls made, which is in the state rather than beside it so a game is reproducible from what crosses the wire. There is no doubling cube; the rules document says so plainly. Mastermind is played as a duel — both players are set a code and both are breaking one — because the pencil-and-paper game gives the codemaker nothing to do. It ends at the foot of a round, never mid-round, or going first would be worth half a guess. It is the one game here with anything to hide, so viewFor does real work: the host sends each device only its own code, and a device that was never given a code refuses to score a guess against it rather than quietly answering "nothing". Pirates and Bulgars is Sackson's theming of Asalto, and the rules document is explicit about which parts are attested and which had to be chosen — the book could not be obtained. Two hunters who take by jumping against twenty-four who cannot take at all, on a thirty-three point cross whose drawn lines come from the same adjacency table the moves come from, so the board and the rules cannot disagree. 130 unit tests across the four engines, all run locally as well as in CI: game/ has no Android in it, which is what makes that possible. Co-Authored-By: Claude Opus 5 <[email protected]> Claude-Session: https://claude.ai/code/session_019Pr6B8xDDtJJcb6WJMw7Ud
97 lines
4.2 KiB
Markdown
97 lines
4.2 KiB
Markdown
# Backgammon
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Twenty-four points, fifteen checkers a side, and two dice. Bring everything
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round to your home board and bear it off before your opponent does.
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## The board
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Points are numbered 1 to 24. **White runs down the numbers and bears off past
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1; Black runs up them and bears off past 24.** White's home board is points 1–6,
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Black's is 19–24.
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A point belongs to whoever has two or more checkers on it, and is closed to the
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other player. A point with exactly one checker on it is a **blot**, and can be
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hit.
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## The opening
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Each player throws one die and the higher number starts, playing both dice as
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thrown. A tie is thrown again, so the game never opens on a double.
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## A turn
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Throw two dice and move one checker for each. **A double is four moves**, not
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two.
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The rule that decides most disputes is this one: **you must use as much of the
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roll as you can.** If there is a way to play both dice, you must play both, even
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when playing one would suit you better. If only one can be played, it must be
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the higher one. The app enforces this by working out every way the whole roll
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could be played before offering you anything, so a move that would strand the
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other die is simply never on the board. That is why a legal-looking move
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sometimes cannot be tapped: playing it would waste half your roll.
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## Hitting and the bar
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Landing on a blot sends it to the bar. A player with a checker on the bar must
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bring it back on before moving anything else, entering in the opponent's home
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board: White enters on 24 minus the die, Black on the die itself. If every entry
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point is closed the turn is lost, and it can be lost several times over.
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## Bearing off
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Once all fifteen checkers are in your home board you may start bearing off. An
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exact die takes a checker off the point that needs it. A bigger die may take one
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off your highest occupied point, but only when nothing is standing further back —
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an overshooting die may never take a checker that a smaller die could have
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reached.
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## Winning
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Fifteen off wins. How much it is worth depends on how badly the loser lost:
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| --- | --- |
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| **Single**, 1 point | the loser has borne at least one checker off |
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| **Gammon**, 2 points | the loser has borne nothing off |
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| **Backgammon**, 3 points | and still has a checker on the bar or in the winner's home |
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Counting gammons is an option. It changes nothing about the moves and everything
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about whether a hopeless game is worth playing out.
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## Not implemented
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**There is no doubling cube.** A single game is played rather than a match to a
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number of points, and with nothing being kept between games there is nothing for
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a cube to double. It is the largest thing missing from this implementation and
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the one a serious player will notice first.
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## The dice
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Every die in the game comes from the table's own seed and a count of how many
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rolls have been made, so a game is reproducible from the state it started in and
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a host and a client can never disagree about what was thrown. The seed travels
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with the state, which is safe: backgammon has nothing hidden, and the host is
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authoritative about every roll in any case.
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## What the computer does
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Not a search in the sense the chess and checkers players are one — there is no
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tree to walk, because the opponent's reply depends on dice nobody has thrown
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yet. Instead it weighs **whole turns**: every distinct way the roll can be
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played, scored by the board it leaves behind.
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Weighing turns rather than checkers is the point. A backgammon move is only good
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in company — splitting the back checkers is right or wrong depending on what the
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other die did — and a player choosing one checker at a time would never see it.
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At the strongest level it also averages what the dice might do to it next: all
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twenty-one distinct rolls, weighted properly (6-5 comes up twice as often as
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5-5), taking the opponent's best answer to each.
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The evaluation is built on the pip count, because backgammon is a race. Around
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that: a blot is only a liability if it can be hit, so exposure is weighted by
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how far away the nearest enemy checker is; a made point in your own home board
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is worth having because it is one more number your opponent cannot come in on;
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and a long run of consecutive points is what traps a checker behind it.
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