or-join too strict? about datalog-parser

[xificurC]

Just to have that datomic example noted:

(require '[datomic.api :as db])
(def c (db/connect (doto "datomic:free://localhost:4334/mydb?password-datomic" db/create-database)))
(db/transact c [{:db/ident :id :db/valueType :db.type/keyword :db/cardinality :db.cardinality/one :db/unique :db.unique/identity} {:db/ident :n :db/valueType :db.type/long :db/cardinality :db.cardinality/one}])
(db/transact c [{:id 1 :n 1} {:id 2}])
(db/q '[:find (pull ?e [*]) :in $ ?max :where [?e :id ?id] (or-join [?e ?max] (not [?e :n _]) (and [?e :n ?n] [(< ?n ?max)]))] (db/db c) 1000)
;; =>
[[{:db/id 17592186245422, :id :b}] [{:db/id 17592186245421, :id :a, :n 1}]]

[whilo]

I think this is an ambiguity in the Datomic specification:

An or-join clause allows you to specify which variables should unify with the surrounding clause; only this list of variables needs binding before the clause can run.

https://docs.datomic.com/on-prem/query.html#building-queries-programmatically

Our parser has interpreted the "should" unify to mean that these variables should also exist in the clauses and unify between them and the outside. Datomic on the other hand says that it will make sure that these variables are bound before the clause is run (a guarantee that we do not make yet), while it seems permissive if they are not being used. I have changed our behavior. The issue is fixed in datalog-parser 0.1.3 in 85a3ca1.

Please open further issues if you experience more inconsistencies.