Conditions

Conditions appear after while, after when, in refuse when, and in blocked exits. The combinators are and, or, and not, in the usual precedence (not binds tightest, or loosest) with parentheses to override; one chance in N rolls dice.

  on petting it
    phrase cat-tolerates when it is dozing
    phrase cat-glare when it is alert and not one chance in 4
    phrase cat-purr when (it is alert and one chance in 4) or it wears the ribbon
    change it to alert when it is dozing
  end on

The predicates test what an author would point at:

  on examining it
    phrase barrow-contents when it holds the apple
    phrase barrow-visible when the player can see it
    phrase barrow-in-gate when it is in the Orchard Gate
    phrase barrow-is-thing when it is a container
  end on

In full: is a/is an tests kind or trait, is in tests location, is here tests whether an entity shares the player's location, plain is compares against a state, a state adjective, or a value, has, holds, and wears test possession, and can see / can reach test scope. Every predicate takes not after is, or not in front. Subjects and values are written the way you name anything: it, the player, an entity name, its <field>, or a possessive like the player's location. A multi-word name simply runs until the next structural word (is, has, holds, wears, can, and, or, then, to, while, with), so name your entities around those.

State words resolve against their subject: when it is dozing works because the cat declares dozing. The closed catalog of platform state adjectives (open, closed, locked, unlocked, on, off, worn, lit) reads trait state the same way. An unknown word is a load error with a nearest-valid suggestion, not a silent false.

A named condition whose it is left free is an open condition: a test any entity might pass. any and no quantify over one:

define condition gathered-tomato: it is a tomato and it is in the harvest basket
define condition vine-tomato: it is a tomato and it is not in the harvest basket

  on examining it
    phrase basket-empty when no gathered-tomato
    phrase basket-laden when any gathered-tomato
  end on

Quantifiers demand an open condition; any over a closed one (no free it, like the story is dusk) is analysis.closed-condition-selection. Inside an open condition, keep to predicates the analyzer can check for an arbitrary subject: kind, placement, and possession tests. A state test on it (it is ripe) is rejected as an unknown value, because no one subject owns the state word there.