Predicate seems to be lazily evaluated and fails silently

[frankiesardo]

Hey @tonsky

I've noticed a behaviour that is substantially different from Datomic, and might be a bug.

I'm using datascript 1.0.3 and I've tested this behaviour both on cljs and clj.

When I'm running

(d/q '[:find ?name ?result
       :in $ ?my-fn
       :where
       [?e :person/name ?name]
       [(?my-fn) ?result]
       [(< ?result 3)]]
     (d/db-with (d/empty-db) [{:person/name "Joe"}])
     (fn [] 5))

=> #{}

I correctly get an empty set (result is greater than 3)

But if I do not force the evaluation of ?result the condition is never checked

(d/q '[:find ?name
       :in $ ?my-fn
       :where
       [?e :person/name ?name]
       [(?my-fn) ?result]
       [(< ?result 3)]]
     (d/db-with (d/empty-db) [{:person/name "Joe"}])
     (fn [] 5))

=> #{["Joe"]}

The same behaviour occurs on the JVM if you call the function directly

(defn my-fn [] 5)

(d/q '[:find ?name
       :in $
       :where
       [?e :person/name ?name]
       [(user/my-fn) ?result]
       [(< ?result 3)]]
     (d/db-with (d/empty-db) [{:person/name "Joe"}]))

=> #{["Joe"]}

The equivalent code in Datomic produces an empty set instead.

(def conn (do (d/create-database "datomic:mem://test") (d/connect "datomic:mem://test")))
(defn my-fn [] 5)

(d/q '[:find ?doc
       :in $
       :where
       [?e :db/doc ?doc]
       [(user/my-fn) ?result]
       [(< ?result 3)]]
     (d/db conn))

=> #{}

[tonsky]

Looks like a bug — I’ll take a look!

[tonsky]

Pushed 1.0.5, hope it fixes the issue

[frankiesardo]

It does, thanks for the quick fix! 🥇