A recursive call to union() would interfere and prevent value observers
to be propagated to the new root. This causes, among other things, a failure
to reactivate certain constraints.
In case evaluation fails and the state of activated occurrences is
reset to some previously stored state, the trace view does not
get updated and contains some stale information. This patch fixes it.
A propagaition rule must ignore reactivated occurrence.
Although it is possible that other occurrences are waiting,
and they can be erroneously selected if precautions are not taken.
The default tell protocol assumes an exception is to be thrown
in case predicate is not satisfied. This may lead to unnecessary
exceptions being thrown in a situation where a simple failure
status would have been sufficient.
Introduce feedback basis to track dependencies on rules.
Index journal chunks by evidence for quick lookup.
The feedback basis is the collection of principal rules tags
from the justifications of the current match.
For this several notions are introduced.
Logical variable is called "principal" if it is used in principal
occurrences and at some point during evaluation is unified or bound.
Principal occurrence is called "volatile" if it uses principal logicals.
PrincipalObserverDispatcher's task is to track volatile occurrences
by enabling uni observers on all free logicals in principal occ-s.
RewindVolatileOccurrencesStage then on events of incremental usage
of volatile occurrences (e.g. match on it, or continued activation)
resets journal cursor to the position of initial occurrence activation,
where it can be re-evaluated with fresh, unaffected, logicals.
It's the only stage that goes backwards in journal.
So in this way unification is incrementally cancelled.
link to MPSCR-62 (docs)
Rename NonIncrementalProcessing -> DefaultProcessing
Add GroundProcessing as common superclass to handle OccurrenceContractObserver
Add another test for this occurrence contract logic.
Fedor Isakov