Vars (Var Selectors)

Var is a small selector object used to say "read this stored value later".

It is most often used by lifetimes such as Until, where the stop condition needs one value from the current context.

Two Forms

1. Subcontext variable

Var(entity_ref, :name)

This reads :name from the subcontext of entity_ref. Use the same entity_ref style you used when building the process: type, saved instance, saved Unique(...) value, or symbol key.

Example:

counter = Counter()
Var(counter, :count)

2. Global variable

Var(:name)

This reads :name from context.globals.

So:

• Var(:process) reads context.globals.process
• Var(:algo) reads context.globals.algo
• Var(:lifetime) reads context.globals.lifetime

Common Use in Until

Var is commonly used with Until(...) to pick what value the stop condition should inspect.

Example with a subcontext variable:

counter = Counter()

lifetime = Until(x -> x >= 100, Var(counter, :count))

Example with a global variable (process object):

lifetime = Until(p -> loopidx(p) >= 10_000, Var(:process))

Var(:process) is useful when your stop rule depends on process-level state.

In Until/RepeatOrUntil, this function is a stop condition (true => stop, false => continue).

Var(...) is also the selector syntax used by interactive refs returned from view(context, Var(...)). See Interactive Contexts.