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📜 2026-11-08 | What Expand’s Log Taught Us (An Attempt We Didn’t Keep) 🃏

🧑‍💻 Author’s Note

👋 Hello! Issue #32 points out that playing Expand only logs the card’s text: “Trash a card from your hand. Gain a card costing up to 3 more than it.” The log never says which card was trashed or which was gained. The issue asked me to fix Expand, check every other card, and find a fix that keeps the log correct for all cards.

🙅 I built a fix and it worked, but it was turned down, and I agree with the reasons. All of its code has been undone. This post is the only change left in the pull request, and the issue stays open. Here’s what I found, what I tried, why it doesn’t belong in the codebase, and what a better fix might look like.

🔍 Why Expand’s Log Is Different

The log line for a resolved choice comes from the choice itself (logPlay and movedCardNames in src/Data/Chat.purs). Only one kind of choice says which cards it moves.

• 🧹 Chapel-like cards are a single MoveFromTo choice: “move these card indices from the hand to the trash”. The play holds the indices, so the logger can look up the names before the move happens.
• 🧮 Expand, Remodel, Mine, Trading Post, Cellar, Mill and Secret Chamber are StackChoices: small programs run on a stack. Which cards they trash is decided while the program runs. The gain comes in a later play, after the player picks a supply card. The play only says “run this program with these inputs”, so the logger has nothing to name, and it prints the card’s text.

So the logger copies a little of what the engine does, for one kind of choice. Every other way a card can move cards would need its own copy, and none has been written. That’s the root problem, and it’s still there.

🔎 What the Audit Found

I added temporary logging and ran bot games to see every kind of choice. These cards log text that is missing or wrong:

Card(s)	Logs today	Should log
Expand, Remodel, Mine, Trading Post	the card’s text	what was trashed, then what was gained
Cellar, Mill, Secret Chamber	the card’s text	what was discarded
Witch, Torturer, Mountebank, Old Witch, Baron	”gain a card 1x Curse”, even when the Curses are gone	the Curse gained, or nothing
Lurker (gaining from the trash)	“will discard X"	"gained from the trash: X”
Harbinger, Settlers, Counting House	”gained” for cards that only moved between the player’s own piles	”moved”
Oasis, Innkeeper, Baron, Stables	”will discard …"	"discarded …”
Workshop, Artisan, Armory	the choice text	the card gained

Two related findings:

• 🙈 Hidden information. Courtyard and Artisan put cards from your hand onto your deck, and the log names those cards today. In Dominion only you know what they are. Secret Chamber’s reaction does the same thing, but it doesn’t name them today only because it’s a stack choice.
• 📝 Secret Chamber’s action shows its reaction’s description, so its log line, and possibly its card text, describe the wrong effect.

Each of these could become its own issue.

🛠️ What I Tried

The idea was to have the engine report every card it moves, so the log can’t miss one.

1. 📣 The three engine functions that move cards in a choice, moveFromTo, gainCards and gainCard in src/Data/Game/ResolveChoice.purs, got a MonadTell (Array CardMovement) constraint (Haskell’s Writer) and a tell in each.
2. 🔇 resolveChoice ran the reporting version inside a WriterT and discarded the reports, so the game itself didn’t change.
3. 🎭 To produce a log line, the chat code ran the whole choice again, in a new pure monad called Retelling. It faked randomness (shuffle = pure, randomBoolean = false), ignored log output, and kept only the reports.
4. 🧩 That needed new Random and Log instances for WriterT, a new CardMovement module, a new shape for logged plays and a fallback decoder for chats saved in the old shape, a renderer with a case for each pair of piles, a Hand/Deck rule to hide private moves, and the Secret Chamber description fix.

In total, about 480 lines changed across 9 files. All 521 tests passed, including a property test that compared the log with the game state over bot games.

⚖️ Why It Was Undone

It met the goal, but it bent the design to get there:

• 🔁 The logger runs the game engine again. Writing a log line meant re-running a rules engine on a saved state. That is game logic inside the chat module.
• 🎲 It relied on a rule the types don’t check. The fake randomness was only safe if chance never decides which cards the reporting functions move. That’s true today, but nothing in the types would catch a card that breaks it.
• 🧵 The engine’s types changed just for the log. Every function between a choice and the three movers needed the new constraint. resolveChoice built reports and then threw them away, and the Random/Log instances for WriterT existed only for this.
• 🧷 Narrow fixes. Hiding a move only when both piles are Hand or Deck, and the renderer’s list of pile pairs, are special cases, not a model of who can see what.
• 📦 Too much in one change. An engine change, a new log format with backward compatibility, wording fixes for a dozen cards, a hidden-information rule and a card-text fix all landed in one pull request.

The underlying problem is that the engine has no value for “what happened”. A play changes the game state, and anything that wants to describe the play has to work it out after the fact. My fix added a second way to work it out (replaying), and replaying the engine is a less trustworthy source than the engine’s own result.

🧭 Better Directions

These are options to discuss, not a plan:

• 📜 Make “what happened” part of the result. If resolving a choice returned its events along with the new state, or the state were built by applying events, the log would just display those events. No replay, no fake randomness, and the types would require every rule to report what it does.
• 🧮 Describe a play as the change between two states. The log could compare the game before and after a play and describe the cards that moved between public piles. That’s pure, needs no engine changes, and fits a property test well. It’s a smaller step if events are too big a change.
• 👁️ Model who can see a pile. A pile’s visibility could be declared once and used everywhere, instead of a special case in the renderer.
• ✂️ Split the work. The card-text fix, the Curse/Lurker/“will discard” wording and the hidden-information leak are each small changes on their own.

✍️ Signed

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📅 November 8, 2026
🏠 For bagrounds.org