Poor man's JavaFX Script is, er... Javascript

Sun has release its own RIA framework called Java FX. It provide JavaFX Script, which is a language based on Java whose goal is to develop quickly graphical applications with the power of Java. Is it touted as competition to Flex that I have mentioned before. It is safe to say that it hasn't been received with a great deal of enthusiasm. The fact is, I don't want to learn another language again to do my Web 2.0 application. And I do believe that Fielding has a point when he reflects that applets break visibility and raise the barrier of entry for web developers. Also, I'm usually all in favor of static typing and compilation, but for GUIs I'm not too sure. When you want to tweak your borders or your layouts you probably happy enough with a quick cycle of change code/refresh page. So why don't we use Javascript and Java Applets together instead of inventing yet another technology?
Ok, it's time you get over your irrational distrust of Javascript. A multi paradigm (object, functional) language available for free in every browser!! And no, I don't suggest we go on using the HTML DOM or things like that. That's why we need applets.
Applets? I must be mad! Applets have not worked on the web. But what I suggest is not to develop one applet for each RIA application, but only develop one Applet that everybody could use, much like a plugin, that would bridge the gap between the JavaScript world and the Java/Swing world. If it has been done, please let me know. As for me, I've put together a prototype in an hour that works fine:

1. The JavaScript code constructs an object tree that represents the GUI.
   
2. The object tree is serialized to JSON and passed on to the applet
3. The applet deserializes the JSON and constructs a Swing GUI by translating the object tree
4. The object tree can contain handlers that are the names of Javascript functions
5. The applet calls the javascript functions on Swing events
6. The JavaScript event handlers update the GUI tree and notify the applet with the changes.

A very simple example:

<html>
<head><title>JSApplet</title>

<script language="Javascript">

var helloButton={type:"button","id":"helloButton","text":"hello","action":onClickHello}
var frame={"contents":
 [
  helloButton
 ]
 };


function onClickHello(){
 helloButton.text=helloButton.text.toUpperCase();
 updateJS([helloButton])
}

function startJS(){
 var msg=document.getElementById("JSApplet").setContent(toJSON(frame));
 if (msg){
  alert(msg);
 }
}

function updateJS(objs){
 var msg=document.getElementById("JSApplet").updateContent(toJSON(objs));
 if (msg){
  alert(msg);
 }
}


toJSON=function(arg) {
    
    switch (typeof arg) {
    case 'object':
        if (arg) {
            if (arg.constructor == Array) {
                var o = '';
                for (var i = 0; i < arg.length; ++i) {
                    var v = toJSON(arg[i]);
                    if (o) {
                        o += ',';
                    }
                    if (v != null) {
                        o += v;
                    } else {
                        o += 'null,';
                    }
                }
                return '[' + o + ']';
            } else if (typeof arg.toString != 'undefined') {
                var o = '';
                for (var i in arg) {
                    var v = toJSON(arg[i]);
                    if (v != null) {
                        if (o) {
                            o += ',';
                        }
                        o += toJSON(i) + ':' + v;
                    }
                }
                return '{' + o + '}';
            } else {
                return;
            }
        }
        return 'null';
    case 'unknown':
    case 'undefined':
    case 'function':
     return arg.name;
    case 'string':
        return '"' + arg.replace(/(["\\])/g, '\\$1') + '"';
    default:
        return String(arg);
    }
}

</script>
</head>
<body onload="startJS();">
<applet id="JSApplet" alt="JSApplet" code="fr/moresmau/jp/jsapplet/JSApplet.class" codebase="bin" mayscript="mayscript" height="100" width="100"></applet>



</body>
</html>

This web page creates a simple "Hello" button that when clicked changed its text to upperCase(). It demonstrate the two ways communication between the Javascript code and the applet (note how the function is serialized in JSON just with its name, that's the only thing we need). So the Javascript can deal with a model that is a slightly abstracted Swing model (no more hair pulling between different browsers). I stress again, the applet is a generic applet that deals with the link between the JSON objects and the Swing layer. Of course the applet could offer other services: simple API to call back the server (AJAX from the applet), etc...
Then the applet could be packaged with a cut down version of the JRE (only the classes really needed) as a plugin to do rich Swing application from JavaScript...
And voilà! A scriptable RIA platform!

Haskell code, Java UI

It's been while since I've posted anything, mainly because work crises and holidays have kept me busy or away from my keyboard. I'm still playing with Haskell and user interfaces, I've now developed the same Maze game in HGL, Flex with a Haskell web back end, and WXHaskell. I've looked at trying to implement some declarative syntax that would simplify WXHaskell code but haven't gone very far, I think I'm trying to run in Haskell before I can walk straight!
Anyway, I was looking at Business Objects' Quark framework based on the CAL language. You can find more details here, but basically CAL is a Haskell-inspired impure functional language implemented in Java, that can use Java classes and methods. The impurity comes from not using monads to access Java, if I understand well, which means that you can declare pure functional methods that in fact access Java objects, that can do all kind of stateful voodoo under the covers. While I'm not sure this is really A Good Thing, having Haskell and Java intertwined brings some interesting ideas in the realm of Haskell UIs. Swing and Java are now mature, reasonably fast and cross platform. If I can get my pure Haskell code to talk to a Java GUI, I could get quite happy indeed...

A Haskell GUI in Flex

In an earlier post I mentioned a little Haskell game I developed where you had to navigate in a maze. I used HGL as the GUI framework, and noted it wasn't very clear what was the functional GUI framework of choice for Haskell. So I decided to give Flex a go and to hook it up with my Haskell back-end. I'm quite please with the result, I have to say.
The setup is as follows:
1) I've implemented a very simple single-threaded HTTP server in Haskell, using as an inspiration code that I found here and there (using Parsec for parsing HTTP messages, etc.). The server can server static HTML and SWF files as well as having a dynamic component: you can register Haskell methods that take a JSON object as a parameter, some internal state and return a new JSON object and the new state (yes I know, there is a monad for that...). I used the code here for JSON in Haskell. I thus expose a method that generates a Maze and a method to move to a cell, validating that there is no wall in between the current cell and the target cell and checking to see if we reached the exit.
2) I use Flex and ActionScript to create the GUI. The compiled SWF file will be served by the Haskell server and will call it back through asynchronous calls. I was a bit taken aback when I realized that Flex doesn't come with JSON support out of the box, but luckily there's a library for it. So you connect via your browser to a page on the server that embeds the SWF, Flex ask for the maze data to the server and displays it, and let you navigate using the keyboards or the mouse.
And that's it! So I have a nice, platform independent GUI and functional business code. I was thinking, who needs a special GUI framework for the desktop when an application could be made easily with a very lightweight local HTTP server and a web based interface? I even thought that Flex was a bit too much: why do I need a GUI technology that requires compilation when I can do nice stuff with pure HTML/Javascript frameworks like Dojo? So I can use a UI technology that is purely for UIs, and a functional language with the goodies Haskell provide for all the back-end, computation-heavy work.
The code for Haskell is here (start from Framework.hs), the Flex code is here.

Haskell User Interface???

It's been a long time since I've last posted, the fault to Christmas and holidays. In the meantime though I have done some more Haskell. I have used Prim's algorithms described here to generate a random maze. That forced me to use Random to generate the maze and HGL to display it, and allow the user to navigate from the entrance to the exit with direction keys. Works great, but I was looking at Haskell UIs to see what I could use, and there doesn't seem to be a consensus on a functional GUI library in Haskell. HGL is fairly low level and limited, wxwidgets ports have an imperative air about them and some of the ground breaking frameworks still seem to be experimental (and to be honest, I don't think I'm ready to deal with arrow-based frameworks yet, I'm still struggling with the monads...). So maybe the solution is elsewhere? I've seen in the Java world people talk about Flex, has anybody done anything integrating a Flex front end with a Haskell back-end?