Default Viewer

If you would like to add some logic around which viewer to use by default in Portal, the easiest way is to provide a :portal.viewer/default key as part of a value's metadata. Unfortunately, not all values support metadata, such as strings. They way around this limitation is to wrap the value in a container that does support metadata, such as vectors.

Here is on such default viewer selector:

(def defaults
  {string? :portal.viewer/text
   bytes?  :portal.viewer/bin})

(defn- get-viewer [value]
  (or (some (fn [[predicate viewer]]
              (when (predicate value)
                viewer))
            defaults)
      :portal.viewer/tree))

With a corresponding submit function:

(require '[portal.api :as p])

(defn submit [value]
  (p/submit
   (with-meta
     [(get-viewer value) value]
     {:portal.viewer/default :portal.viewer/hiccup})))

(add-tap #'submit)

Now by tapping the following values you can see the default viewer selector in action:

(tap> "hello, world")
(tap> (byte-array [0 1 2 3]))
(tap> (range 10))