Match by attribute namespace

[alex-dixon]

When we have attributes that share the same namespace, e.g.:

:explanation/rule
:explanation/bindings
:explanation/facts
:explanation/matches

it would be handy to match on "explanation". We do not currently allow this. For one, ":a" must be a keyword. It might get too crazy even for us if we endeavored to support a function in this slot, though it would allow dynamic type matching. That may not be possible without rewriting the rule using a macro, as I'm not sure Clara supports this directly.

We could match on attribute namespace within a rule with the syntax explanation/* by adding the necessary logic to our default fact-type function.

[alex-dixon]

An alternative may be to establish a hierarchy/ancestry for namespaced keywords.

Example:

:explanation.rule/ns
:explanation.rule/name
:explanation.rule/lhs
:explanation.rule.conditions/constraint

(define [?e :rule-explanation ?explanation] 
  :- [[?explanation <- (acc/all (juxt :a v)) :from [?e :explanation.rule]]

Advantages:

• Might be easier to implement (depends on how much we're using the ancestry data structure vs. the ancestors function, which allows an arbitrary predicate like ":explanation.*")
• Might be more performant than converting keywords to strings etc

Disadvantages:
Not as much of a visual indication that a hierarchical match is taking place, though Clojure's idiom of "leaf" namespaced attributes containing / does provide this information

With either approach we would match on something like explanation.rule.condtions/constraint that could have 1000x more facts than the ancestors at the depth level above. If we wanted to support direct descendant matching only, a variant on the keyword + * syntax could be provided. Not clear how we could represent something like first descendants with a namespaced keyword hierarchy.