Wednesday, July 24, 2013

New push mode, to present data in real time. in MFlow

Another milestone completed in MFlow.  The new asynchronous widgets can display server information at the moment that they appear. And thanks to Software Transactional Memory this may be immediately.

The new primitive, push, like autoRefresh,  is a modifier of a widget behavior. In this case push  will execute the widget and present the output again and again using ajax internally. This is an example:

http://mflowdemo.herokuapp.com/noscript/push


 
 
The image is not very exciting. I will try to add another better. In this example the push widget is above the text box.
 
The code is as follows:
 
pushSample=  do
  tv ←  liftIO $ newTVarIO $ Just "The content will be appended here"
  page $   h2 << "Push example"
       ++> p << "The content of the text box will be appended to the push widget below."
       ++> p << "A push widget can have links and form fields."
       ++> p << "Since they are asynchronous the communucation must be trough..."
       ++> p << "The input box is configured with autoRefresh"
       ++> hr

       ++> pageFlow "push" (push Append (disp tv) <** input tv)
       **> br
       ++> br
       ++> wlink () << b << "exit"

  where
  -- the widget being pushed:
  disp tv= do
      setTimeouts 100 0
      line ←  tget tv
      liftIO $ when (line ≡ "kill") $ myThreadId ↠ killThread
      p <<  line ++> noWidget

  -- The input box
  input tv= autoRefresh $ do
      line ←  getString Nothing <** submitButton "Enter"
      tput tv line


  tput tv x = atomic $ writeTVar  tv ( Just x)

  tget tv= atomic $ do
      mr ←  readTVar tv
      case mr of
         Nothing → retry
         Just r → do
          writeTVar tv Nothing
          return r

atomic= liftIO . atomically

There are still some minor issues with this widget, but I expect to fix them soon. As you can see, the push widget retry when Nothing is available in the TVar. When the input widget tput's something in the variable, it is read, emptied and returned to be displayed. The other widgets of the  page must be configured with autorefresh, unless we want to navigate away from the page. This is why the text input box and the button are under autoRefresh, but the exit link is not.

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