External predicates #59
Description
It would be desirable if from within evaluation, "external" predicates could be queried which retrieve data.
- they would require a Decl with a mode declaration (some positions input, others output) and
- they do not need to be extensional predicates (they may do computation on other facts).
- functional dependency is not required (there can be many outputs for the same input)
- determinism has to be assumed: once an atom is evaluated for inputs, the "output relation" does not change.
- thus, the store acts as a cache. For an input-tuple, the external predicate hook can only be invoked once.