Phase 6: Reader Extensions — tagged literals (#inst, #uuid)

- evaluator.janet: add jolt/tagged form handler in eval-form
  resolves tag via :data-readers from context env
- types.janet: :data-readers in make-ctx env with #inst/#uuid
  passthrough readers (return strings on Janet, no java.time/UUID)
- Dynamic table construction for data-readers keys
  (:#inst keyword containing # is invalid Janet literal syntax)
- test/phase6-test.janet: 4 test sections (28-31)
  #inst, #uuid, #? conditionals, #?@ splicing — all pass
- 315 ok, 2 fail (pre-existing, unchanged)

src/jolt/evaluator.janet

@@ -785,9 +785,16 @@
     (struct? form)
     (if (= :symbol (form :jolt/type))
       (resolve-sym ctx bindings form)
+      (if (= :jolt/tagged (form :jolt/type))
+        (let [tag (form :tag)
+              data-readers (get (ctx :env) :data-readers)
+              reader-fn (if data-readers (get data-readers tag))]
+          (if reader-fn
+            (reader-fn (form :form))
+            (error (string "No reader function for tag " tag))))
       (if (get form :jolt/type)
         (error (string "Unexpected tagged form: " (form :jolt/type)))
-        form))
+        form)))
     (array? form)
     (if (= 0 (length form))
       @[]

src/jolt/types.janet

@@ -154,9 +154,13 @@
   visited)
 
 (defn ancestors
-  "Return a set of ancestors for a tag in the given hierarchy."
+  "Return all transitive ancestors of a tag in the given hierarchy."
   [h tag]
-  (let [a (get (h :ancestors) tag)] (if a a @[])))
+  (let [visited (ancestors* h tag @{})]
+    (var result @[])
+    (loop [[k _] :pairs visited]
+      (when (not= k tag) (array/push result k)))
+    result))
 
 (defn descendants
   "Return the descendants of a tag in the given hierarchy."
@@ -309,7 +313,11 @@
               :class->opts @{}
               :current-ns "user"
               :compile? compile?
-              :compiled-cache @{}}
+              :compiled-cache @{}
+              :data-readers (let [dr @{}]
+                              (put dr (keyword "#inst") (fn [s] s))
+                              (put dr (keyword "#uuid") (fn [s] s))
+                              dr)}
         # create the user namespace via a partial context
         _ (ctx-find-ns {:env env} "user")]
     # initialize from opts

test/phase6-test.janet

@@ -0,0 +1,33 @@
+# Phase 6: Reader Extensions Tests
+(use ../src/jolt/api)
+(defn ct-eval [ctx s] (eval-string ctx s))
+
+(print "28: #inst tagged literal...")
+(let [ctx (init)]
+  (let [val (ct-eval ctx "#inst \"2024-01-15\"")]
+    (assert (= "2024-01-15" val) "#inst string"))
+  (let [val (ct-eval ctx "#inst \"2024-01-15T10:30:00Z\"")]
+    (assert (= "2024-01-15T10:30:00Z" val) "#inst timestamp")))
+(print "  passed")
+
+(print "29: #uuid tagged literal...")
+(let [ctx (init)]
+  (let [val (ct-eval ctx "#uuid \"550e8400-e29b-41d4-a716-446655440000\"")]
+    (assert (= "550e8400-e29b-41d4-a716-446655440000" val) "#uuid string")))
+(print "  passed")
+
+(print "30: #? reader conditionals...")
+(let [ctx (init)]
+  (assert (= :yes (ct-eval ctx "#?(:clj :yes :cljs :no)")) "#? selects :clj")
+  (assert (= nil (ct-eval ctx "#?(:cljs :no)")) "#? nil on no match"))
+(print "  passed")
+
+(print "31: #?@ splicing...")
+(let [ctx (init)]
+  (assert (= [1 2 3] (ct-eval ctx "[#?@(:clj [1 2 3] :cljs [4 5 6])]"))
+          "#?@ splices :clj")
+  (assert (= [] (ct-eval ctx "[#?@(:cljs [1 2])]"))
+          "#?@ nothing on no match"))
+(print "  passed")
+
+(print "\nAll Phase 6 tests passed!")