Viewers

A viewer takes a value and renders it to the screen in a meaningful way. Since a value can be visualized in various ways, there are usually multiple viewers to choose from for a single value.

Viewers can have a :predicate function to define what values they support, so viewers are automatically filtered based on the value.

The bottom-left dropdown displays the viewer for the currently selected value and contains all supported viewers for that value.

Note You can also switch viewers via the portal.ui.commands/select-viewer command.

Default Viewers

Since the default priority order specified in Portal might not be desired, a default viewer can be set via metadata.

For example:

(tap> ^{:portal.viewer/default :portal.viewer/hiccup} [:h1 "hello, world"])

Or for a dynamic value:

(def hiccup [:h1 "hello, world"])

(tap> (with-meta hiccup {:portal.viewer/default :portal.viewer/hiccup}))

Tips

String Values

For values that don't support metadata, such as strings, you can leverage the hiccup viewer.

For example, given a markdown string, you could do the following:

(def md-string "# hello, world")

(tap>
 (with-meta
   [:portal.viewer/markdown md-string]
   {:portal.viewer/default :portal.viewer/hiccup}))

The also illustrates an important aspect about the hiccup viewer, it support traditional html and portal viewers as markup.