Constants in the foreighn key constraints

Hi team.
Latest time we faced several issues which wouldn't arise provided we have
possibility to use constants in foreign key constraints.
brief example where it would be helpful:

table_a
( id uuid,
parent_id uuid,
is_deleted boolean
)
having possibility of FK (parent_id, false) to (id, is_deleted)
would disallow setting parent record deleted flag to true if they have
children, or insert record with is_deleted = true parent.

Regards,
Aliaksei.