fish-rules

The rules engine for Fish, a six-player team card game of asking, deduction and calls, as specified by the Canonical Ruleset v1.1. It is the foundation of the Fish benchmark.

• Deterministic. A game is its seed and its actions: replaying them gives the same states and records on any machine, with a frozen, documented random-number scheme.
• Immutable. apply(state, action) returns a new state and the records the action produced.
• One projection. fish_rules.view.project decides what each seat may see, and is the only way information reaches a player.
• Standard library only, typed, and tested to 100% branch coverage.

from fish_rules.engine import apply, legal_actions
from fish_rules.state import new_game

state = new_game(42)
action = legal_actions(state, state.current)[0]
state, records = apply(state, action)

Layer 1 (fish_rules.deduce) works out, exactly, which seats could hold each card given everything one seat has seen and remembers. This plays part of a random game and prints the cards seat 3 can place for certain:

from fish_rules.cards import card_name
from fish_rules.deduce.tracker import Tracker
from fish_rules.engine import replay
from fish_rules.playout import random_game
from fish_rules.view import latest_event, project

tracker = Tracker(3)  # what seat 3 can work out, remembering everything it is shown
last = None
for state, records in replay(42, random_game(42, 7)[:150]):
    last = latest_event(records, last)
    deduction = tracker.observe(project(state, 3, last))

for card in range(54):
    seat = deduction.known(card)
    if seat is not None and seat != 3:
        print(card_name(card), "is with seat", seat)

Install with pip install fish-rules (Python 3.14 or later). For a multi-agent environment built on it, see fish-env; for baseline agents, fish-agents. Documentation, including the frozen encodings, is in the repository.

Licensed under Apache-2.0.