Add (currently unused) ability to generate CTEs.

src/datomish/query/cc.cljc

@@ -65,6 +65,7 @@
             known-types       ; {?var1 :db.type/integer}
             extracted-types   ; {?var2 :datoms123.value_type_tag}
             wheres            ; [[:= :datoms123.v 15]]
+            ctes              ; {:name {:select …}}
             ])
 
 (defn bind-column-to-var [cc variable table position]

src/datomish/query/clauses.cljc

@@ -255,6 +255,7 @@
          :extracted-types {}
          :external-bindings (or external-bindings {})
          :bindings {}
+         :ctes {}
          :wheres []})
       patterns)))
 
@@ -265,6 +266,8 @@
   [cc]
   (merge
     {:from (:from cc)}
+    (when-not (empty? (:ctes cc))
+      {:with (:ctes cc)})
     (when-not (empty? (:wheres cc))
       {:where (cons :and (:wheres cc))})))