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.

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.