exists

exists <value>

Whether a value is present — not null, and, for an entity reference, still pointing at a live entity.

For a creature, object, or room reference, exists checks that the entity the reference names is still in the world. A reference to a creature that has since been extracted, for example, is not live, so exists reports false even though the reference itself is not null.

Arguments

Returns

A bool — true unless the value is null or a stale entity reference.

Examples

after command (say) {
  require [exists $actor]
  do "say I can tell that $actor is really here."
}

The guard lets the handler run only when $actor resolves to a live creature; otherwise the script advances to the next matching handler (see require).

after command (say) {
  let target [first [creatures $self]]
  do "say exists=[exists $target]."
}

When at least one creature shares the owner's room, [first ...] yields a live creature and [exists $target] is true; in an empty room first yields null and exists is false.

See also