Define conj-in, a conjing variant of assoc-in.

src/datomish/util.cljc

@@ -17,3 +17,15 @@
            (str/starts-with? (name x) "?"))
     (keyword (subs (name x) 1))
     (raise (str x " is not a Datalog var."))))
+
+(defn conj-in
+  "Associates a value into a sequence in a nested associative structure, where
+  ks is a sequence of keys and v is the new value, and returns a new nested
+  structure.
+  If any levels do not exist, hash-maps will be created. If the destination
+  sequence does not exist, a new one is created."
+  {:static true}
+  [m [k & ks] v]
+  (if ks
+    (assoc m k (conj-in (get m k) ks v))
+    (assoc m k (conj (get m k) v))))