Hierarchical data core.logic

[dan.sto...@gmail.com]

I think this is a dummy question, but wondering whether this is possible in core.logic?

Lets say I have a set of relations

(db-rel foo p)

(db-rel bar p)

(db-rel fooz p p2)

and facts

[foo 1]

[bar 2]

[fooz 2 1]

[bar 3]

[fooz 3 1]

See that the fooz relation is potentially describing bar as children of foo's. (like a foreign key)

and I want to unify with all the `bar`s for a given `foo` like so:

(run* [?q]

 (fresh [?foo ?bars] 

  (bars-for-foo ?foo ?bars)

  (l/== {:foo ?foo 

           :bars ?bars}

          ?q)))

=>

({:foo 1, :bar (2 3)})

Is it possible to define bars-for-foo?

[David Nolen]

There's no need to define the reverse relation - fooz can do it. Just
supply bar and leave the foo fresh.

David

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[Daniel Stone]

I'm not sure I fully understand, I guess I'm looking for the equivalent to a sub query? When I tried to implement this early, I naively perhaps tried something like this:

(defn bars-for-foo

  [?foo ?bars]

  (l/== ?bars

    (l/run* [?q]

      (fooz ?foo ?q))))

This seems relevant: http://dev.clojure.org/jira/browse/LOGIC-68

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[David Nolen]

Ah sorry I miss read. Not currently supported, it's a requested
feature from Prolog that I haven't gotten around to implementing.

David