(handle-exceptions
        exn (webview-log
             (string-trim
              (call-with-output-string
               (cut print-error-message exn <> "Callback Error"))))
        (proc view data)))))

(define (webview title proc #!key [url #f] [width 800] [height 600] [resizable? #t] [debug? #f] [yield! #f])
  (letrec ([view
            ((foreign-lambda
              webview "webview_new"
              nonnull-c-string c-string int int bool bool)
             title url width height resizable? debug?)]
           [loop
            (lambda ()
              (when (zero?
                     ((foreign-safe-lambda
                       int "webview_loop"
                       nonnull-webview bool)
                      view (not yield!)))
                (cond
                  [(number? yield!)
                   (thread-sleep! yield!)]
                  [yield!
                   (thread-yield!)])
                (loop)))])
    (if view
      (set-finalizer!
       view
       (foreign-lambda
        void "webview_destroy"
        nonnull-webview))

<h3><tt><nowiki>
  (webview? VALUE) ⇒ BOOLEAN
</nowiki></tt></h3>

Predicate for the tagged pointer type representing a web view window.

<h3><tt><nowiki>
  (webview TITLE PROC [#:url URL] [#:width WIDTH] [#:height HEIGHT] [#:resizable? RESIZABLE] [#:debug? DEBUG] [#:yield! YIELD]) ⇒ VOID
</nowiki></tt></h3>

Creates a web view window with the given <tt>TITLE</tt> and runs an
event loop until the user closes the window or termination is requested
using <tt>webview-terminate!</tt>.

The message callback is invoked as <tt>(PROC WEBVIEW STRING)</tt>
whenever a script on the web page calls <tt>window.external.invoke(STRING)</tt>.

If you specify a <tt>URL</tt> that is not <tt>#f</tt>, the page at that
location is loaded into the web view. Otherwise, a blank page is loaded
which sends a <tt>"load"</tt> message when ready and contains a
<tt>&lt;div id="app"&gt;</tt> element that you can fill with custom
content, for example using <tt>webview-inject</tt>.

Window properties may be specified using the <tt>WIDTH</tt>,
<tt>HEIGHT</tt> and <tt>RESIZABLE</tt> keyword arguments. If the
<tt>DEBUG</tt> keyword argument is not <tt>#f</tt> and the platform
supports it, the web view will allow access to debugging tools.

If <tt>YIELD</tt> is not given or <tt>#f</tt>, the event loop will block
the operating system thread when no events are pending. You can set
<tt>YIELD</tt> to a number of seconds sleep period between iterations of
the web view event loop; this reduces responsiveness of the user
interface but allows other CHICKEN threads to run and does not hog the
CPU. You can also set <tt>YIELD</tt> to <tt>#t</tt> to call
<tt>thread-yield!</tt> between iterations of the event loop; this allows
other CHICKEN threads to run without delaying user interface event
processing but will use a lot of CPU cycles.

<h3><tt><nowiki>
  (webview-terminate! WEBVIEW) ⇒ VOID
</nowiki></tt></h3>

Requests termination of the event loop for the given <tt>WEBVIEW</tt>.

dialog is cancelled.

Otherwise, a message dialog is shown and the <tt>#:error</tt> or
<tt>#:warning</tt> flags may be used to switch from an information icon
to a different look. In this case, <tt>VALUE</tt> is the message to
display in the dialog and the procedure will not return a meaningful
result.

The running operating system thread will be blocked until the dialog is
dismissed.

<h2>Logging</h2>

<h3><tt><nowiki>
  (webview-log MESSAGE) ⇒ VOID
</nowiki></tt></h3>