hello. In clara, how can i write recursive queries?

here is an example of the data I have:

{:type :foo
 :desc "'Foo' node"
 :parent :D}

{:type :D
 :desc "'D' node"
 :parent :C}

{:type :C
 :desc "'C' node"
 :parent :B}

{:type :B
 :desc "'B' node"
 :parent :A}

{:type :A
 :desc "'A' node"}

here is what i would like the output of the query to look like:

'(:?node {:type :foo
          :desc "'Foo' node"
          :parent :D}
         
       :?parents [{:type :D
                      :desc "'D' node"
                     :parent :C}

                    {:type :C
                     :desc "'C' node"
                     :parent :B}

                    {:type :B
                     :desc "'B' node"
                     :parent :A}

                    {:type :A
                     :desc "'A' node"}])

is this possible with a clara query?

Not with just a query, you'll need to introduce some facts.

So you'd have one rule that's (heavily abbreviating the code): [:test (no-children? ?node)] => (insert! (->TreeRep ?node ?node))). And one that's [:test (children? ?node)] ?children <- (acc/all) :from [Node (= parent ?node)] => (insert! (->TreeRep ?node (add-children ?node ?children))).

Assuming your graph is acyclic. If it isn't, this will be bad.

It might be doable with one rule, actually. But the point is, AFAICT, there's no way to recurse without inserting facts.

Ah understood.

Will give that a go. Thank you!

Oh, you want to (acc/all) :from [TreeRep ...], probably.

You could also do this with a custom accumulator, but that would be much harder, I'm guessing.

@eraserhd I was thinking along those same lines

about having to introduce some facts to model it

By the way, 👋 clara people! We are starting to rely heavily on this for work, and it is a good thing.