State & verbs: authored traits, custom actions, refusals

An entity state chain

The vine marches forward (seedling, flowering, fruiting) and answers differently at each stage via select on its state:

create the vine
  aka determined vine
  scenery, prunable
  in the Greenhouse
  states: seedling, flowering, fruiting

define trait prunable
  on pruning it
    the player must hold the garden shears: need-shears
    select on its state
      when seedling
        phrase vine-too-young
      when flowering
        change it to fruiting
        move the silver locket to the Greenhouse
        phrase vine-fruits
      when fruiting
        phrase vine-done
    end select
  end on
end trait

The must line is a guard with a named refusal. The flowering arm is the payoff of the boiler chain: when you prune the flowered vine, the silver locket (the deed box's instrument) drops into the world.

Custom verbs

prune isn't a standard IF verb. Two declarations add it: the action (grammar + fallback refusal) and the trait carrying the behavior. The clause that answers a custom verb must live in a trait composed onto the entity, and that is what routes the verb:

define action pruning
  grammar
    prune :target
    trim :target
  the target must be reachable
  otherwise refuse cannot-prune

  phrases en-US
    cannot-prune:
      There's nothing to prune about that.

The case clock works the same way (define action winding, trait windable, wind the clock with the winding key; the endings chapter listens for its chimes).

Authored traits with data

feedable is a story-defined trait with a typed data field (which food this creature accepts) plus its own states and phrases:

define trait feedable
  data
    food: entity
  states: peckish, fed

  phrases en-US
    no-morsel:
      You have nothing that would interest a cat of standing.
    cat-eats:
      The kipper vanishes with terrifying efficiency…

  on feeding it
    the actor must have its food: no-morsel
    it must be peckish: already-fed-cat
    change it to fed
    phrase cat-eats
  end on
end trait

Composed with its field filled in:

create Smoke
  aka cat, grey cat
  a person, follower
  feedable with food the kipper
  in the Pantry

One cat: library follower role (she trails you once met), authored feedable trait (the kipper from Things' tool chain), and a fed-only, once-only hint that noses at where the locket will fall.

Interception: refusing a standard action

Sometimes an entity should veto a verb that normally works. The furnace poker is takeable, until the boiler runs:

create the furnace poker
  in the Boiler Shed

  on taking it while the boiler is running
    refuse poker-hot
  end on

refuse <phrase> stops the action and speaks; the standard TAKE resumes being ordinary the moment the condition clears. The folly door uses the same shape to stay jammed until Tobias has told you its story (on opening it while tobias is not shaken → refuse folly-jammed).