How to add a rule set

Audience       Engine developer.
Prerequisites  `../reference/agents.md`. For a rule that does not
               exist yet, `add-a-rule.md` first.
Result         A new way for a creature to think, picked by its
               tactic.

A rule set is an ordered list of rules. The first one that fires takes the turn.

Step 1: write the set

In models/src/agents.rs, with the other sets:

/// Keeps its distance and shoots; never closes in.
pub static SKIRMISHER: RuleSet = RuleSet {
    name: "skirmisher",
    leashed: false,
    rules: &[SHOOT, KEEP_DISTANCE, STRIKE],
};

Order is the behaviour. Write the set as a sentence first (“shoot if it can, otherwise back off, otherwise bite”) and list the rules in that order.

leashed: true keeps it from stepping out of a room into a doorway or a corridor. Only a set that hunts the player wants it.

Step 2: give it a tactic

A set is picked from the monster’s MovementType in rule_set_for. Add a variant at the end of the enum in models/src/components.rs (a save writes it by position), then one arm:

MovementType::Skirmish => &SKIRMISHER,

The compiler will not build until every match on MovementType has the new arm. Those are the places that still read the tactic directly (the renderer’s tints, the garrote).

Step 3: use it

Put the variant on a bestiary row’s movement column (add-a-monster.md).

Step 4: test it

A unit test in agents.rs per rule the set lists, built on percept(...): one where the rule should win and the ones before it should pass.

Verify

cargo test -p nihilurk-models --lib agents
NIHILURK_SPAWN="your monster" cargo run -p nihilurk

Then add the set’s row to the sets table in ../reference/agents.md.

Appendix: quick check

1. Write pub static <NAME>: RuleSet in models/src/agents.rs; the order of rules is the behaviour.
2. Set leashed: true only for a set that hunts the player.
3. Append a MovementType variant at the end in models/src/components.rs, and add its arm to rule_set_for.
4. Fix every other match on MovementType the compiler names.
5. Put the variant in the movement column of a bestiary row.
6. Test each rule the set lists: one case where it wins, one where an earlier rule passes.
7. Run cargo test -p nihilurk-models --lib agents and NIHILURK_SPAWN="<monster>" cargo run -p nihilurk.
8. Add the set’s row to the sets table in ../reference/agents.md.

See also

add-a-rule.md when no rule does what you need ../reference/agents.md every set, and what picks it ../tutorial/give-a-monster-a-mind.md the same thing, taught slowly