More context in viewers

notebooks/viewers/context.clj

@@ -0,0 +1,44 @@
+;; # 🪬 Viewer Context
+
+(ns viewers.context
+  (:require [nextjournal.clerk :as clerk]
+            [nextjournal.clerk.viewer :as viewer]))
+
+;; A viewer's `:pred` function can perform viewer selection based on a value.
+
+;; It would sometimes be useful to have more context available. Examples of this are:
+;;
+;; * Selecting a viewer based on the originating form
+;; * Selecting a different viewer based on additional context like `:path`
+;; * Bring Clerk's handling of out-of-band metadata like `::clerk/visibility` and `::clerk/width` into userspace
+
+;; To make this a backwards-compatible change, we can opt into these
+;; richer predicate functions using a map with a key:
+
+(def cljc-viewer
+  {:pred {:wrapped (fn [{:keys [form]}]
+                     (contains? (meta form) :cljc))}
+   :transform-fn (fn [{:keys [form]}]
+                   (clerk/eval-cljs form))})
+
+;; We should probably use a namespaced keyword to disambiguate it.
+
+;; Also considered letting the pred function opt in using
+;; metadata. Rejected this because it's invisible and doesn't work for
+;; e.g. keywords.
+
+^::clerk/no-cache
+(clerk/add-viewers! [cljc-viewer])
+
+
+;; Now what can we use this for? We can now, for example, create a
+;; viewer in userspace that evalautes a given form in Clojure and sci,
+;; allowing us to use it on both sides.
+
+^:cljc
+(defn my-greet-fn [x]
+  (str "Greetings from " x))
+
+(my-greet-fn "Clojure")
+
+(clerk/eval-cljs '(my-greet-fn "ClojureScript"))

src/nextjournal/clerk/viewer.cljc

@@ -510,7 +510,7 @@
 
 
 (defn transform-result [{:as wrapped-value :keys [path]}]
-  (let [{:as _cell :keys [form id settings] ::keys [result doc]} (:nextjournal/value wrapped-value)
+  (let [{:as cell :keys [form id settings] ::keys [result doc]} (:nextjournal/value wrapped-value)
         {:keys [static-build? bundle?]} doc
         {:nextjournal/keys [value blob-id viewers]} result
         blob-mode (cond
@@ -522,6 +522,7 @@
                             (select-keys (keys viewer-opts-normalization))
                             (set/rename-keys viewer-opts-normalization))
         {:as to-present :nextjournal/keys [auto-expand-results?]} (merge (dissoc (->opts wrapped-value) :!budget :nextjournal/budget)
+                                                                         (dissoc cell :result)
                                                                          opts-from-block
                                                                          (ensure-wrapped-with-viewers (or viewers (get-viewers (get-*ns*))) value))
         presented-result (-> (present to-present)
@@ -1358,9 +1359,12 @@
               (throw (ex-info (str "cannot find viewer named " selected-viewer)
                               {:selected-viewer selected-viewer :viewers viewers})))
           selected-viewer))
-      (find-viewer viewers (let [v (->value x)]
-                             (fn [{:keys [pred]}]
-                               (and (ifn? pred) (pred v)))))
+      (find-viewer viewers (fn [{:keys [pred]}]
+                             (and (ifn? pred) (if-let [wrapped-pred (and (map? pred)
+                                                                         (ifn? (:wrapped pred))
+                                                                         (:wrapped pred))]
+                                                (wrapped-pred x)
+                                                (pred (->value x))))))
       (throw (ex-info (str "cannot find matching viewer for value")
                       {:value (->value x) :viewers viewers :x x}))))