type.rule_outside_fields: Rule reads something besides its type's fields

Rule reads something besides its type's fields.

Area 2, Values and types; not declinable; the next step is usually the agent's.

A rule reads only its type's fields, so every value of the type follows it wherever it is made, the same in every run: no function of the application, constant, setting, clock or record:

example

type Moment = Instant {}type Booking = Object {    starts: Moment    ends: Moment    rule in_opening_hours: opens_by(starts)}type Opens = Bool {}function opens_by(at: Moment) -> Opens {    return Opens(true)}

jadpo checkcheck failed: 1 error, 1 file

error A rule can't read opens_by(starts)

--> main.jadpo:6:28

  |6 |     rule in_opening_hours: opens_by(starts)  |                            ^^^^^^^^^^^^^^^^ not one of the type's fields

reason: A rule reads only Booking's own fields, with literals, variants, operators, match and the standard operations that give a result from their arguments alone, so every value of Booking follows it wherever it is made, the same in every run.
next: Write the rule over Booking's fields, or check this where the value is built, before building it (agent)
rule: type.rule_outside_fields
help: https://jadpo.dev/docs/errors/type.rule_outside_fields