• ### AJAX in Seaside

So, in yet another post on a series about Pharo and Seaside, I thought I’d highlight a great strength in Seaside: it’s incredibly powerful support for building rich, AJAX-enabled web applications.

As any web developer today knows, if you’re building rich web apps with complex user interactions, you’d be remiss not to look at AJAX for facilitating some of those interactions. AJAX makes it possible for a rendered web page, in a browser, to interact with the server and perform partial updates of the web page, in situ. This means that full page loads aren’t necessary to, say, update a list of information on the screen, and results in a cleaner, more seamless user experience (Gmail was really an early champion of this technique).

Now, traditionally, an AJAX workflow involves attaching Javascript functions to page element event handlers, and then writing those functions so that they call back to the web server using an XmlHttpRequest object, after which the results are inserted into an element on the screen. Of course, doing this in a cross-browser way is pretty complex, given various inconsistencies in the DOM and so forth, and so the web development world birthed libraries like jQuery and Prototype, and higher-level libraries like Script.aculo.us. But in the end, you still have to write Javascript, create server endpoints by hand, and so forth. Again, we’re back to gritty web development. And that makes me a sad panda.

Of course, this post wouldn’t exist if Seaside didn’t somehow make this situation a whole lot simpler, and boy does it ever. To illustrate this, I’m going to demonstrate an AJAX-enabled version of the counter program mentioned in my first post on Seaside. So, instead of doing a full page refresh to display the updated counter value, we’re simply going to update the heading each time the value changes. Now, again, imagine what it would take to do this is a more traditional web framework. Then compare it to this:

renderContentOn: html

| id counter |

counter := 0.
id := html nextId.

html heading id: id; with: counter.

html anchor
onClick: (
html scriptaculous updater
id: id;
callback: [ :ajaxHtml |
counter := counter + 1.
ajaxHtml text: counter.
]
);
url: '#';
with: 'Increase'.

html space.

html anchor
onClick: (
html scriptaculous updater
id: id;
callback: [ :ajaxHtml |
counter := counter - 1.
ajaxHtml text: counter.
]
);
url: '#';
with: 'Decrease'.


That’s it. The full script.

Now, a little explanation. The script begins with a little preamble, initializing our counter, and allocating an ID, which we then associate with the header when we first render it. Pretty standard fare so far. The really interesting bit comes in the anchor definition, and in particular the definition of the onClick handler. Of course, this bit bares a little explanation.

The various tag objects in Seaside respond to selectors that correspond to the standard DOM events. When sending such a message, the parameter is an instance of a JSFunction object, which encapsulates the actual javascript that will be rendered into the document. Now, in this particular example, we’re actually using part of the Scriptaculous library wrapper to create an “updater” object, a type of JSFunction, which takes the ID of a page element, and a callback, and when invoked, causes the callback to be triggered. Upon invocation, this callback is passed an HTML canvas, and when the callback terminates, the contents of that canvas are used to replace the contents of the indicated page element. Neat!

So in this particular case, we have two anchor tags, each of which has an onClick event registered which, when invoked, updates the counter value and then updates the heading on the page.

By the way, there’s also a little bit of extra magic going on here. You’ll notice the ‘counter’ variable is local, while in the original example it was an instance variable. But this works, here, because those callbacks are actually lexical closures, and so the ‘counter’ variable sticks around, referenced by those closures, even though the function itself has returned, and the variable technically has gone out of scope.

To me, the really amazing thing, here, is that never once do I, as a developer, have to even touch HTML or Javascript. The entire thing is written in clean, readable Smalltalk, and it’s the underlying infrastructure that translates my high-level ideas into a functional, cross-browser implementation. Once again, Seaside let’s me forget about all those annoying, gritty little details. I just write clean, expressive Smalltalk code, and it Just Works, exactly as I would expect it should.

Update:

If you want to see the above application running live, you can find it here.

• ### The Seaside Web Framework

While I’m aware that I have, what, maybe two readers of this blog, I thought I might actually start regularly writing a few posts on some of my recent work in the realm of software development. Why? Well, I enjoy writing, and I enjoy… let’s call it “self-gratification”, so posting on my blog seems like a great way to satisfy both of those needs.

So, with all that said, I bring you the kickoff post, covering Seaside.

#### A Little Introduction

Anyone who’s done any amount of serious web development understands what an absolutely horrible place we, as a development community, find ourselves in. We’re still manually authoring HTML, hacking Javascript, writing AJAX callback hooks by hand, and generally doing all the nasty, gritty, ugly work to make rich web applications possible. Of course, frameworks and abstraction layers have come along to make this a bit easier (Google’s GWT is a great example), but in the end, many of us are still stuck in the dark ages when it comes to web development.

Enter Seaside.

Okay, no, wait, let’s back up one step further.

#### A Little Pre-Introduction

You all know what Smalltalk is, right? For those not in the know, it’s a nice, high-level, consistent, clean object-oriented programming language that is really the grandfather for many of the programming languages we see today.

Of course, if that were it, we’d probably all be using Smalltalk today. But, alas, the history of Smalltalk is a messy one, sharing many similarities with the Unix battles of old, plagued by myriad, incompatible, expensive implementations that drove away developers to other solutions.

Furthermore, it’s a little strange in at least one respect: rather than code being stored in files, and compiled into binaries, the entire environment, including all your code, is composed into a single “image” from which you must do all you work, including editing, debugging, and so forth. This has great advantages, for example:

1. The entire environment is available to you and can be inspected and modified as you desire.
2. Deploying an application involves just copying over an image and firing up a VM.

1. You must use the tools provided in the environment (ie, editor, debugger, etc).
2. Integration with version control systems isn’t necessarily that great.
3. It can be tough to figure out where your code ends and the system begins.

So the picture is certainly mixed. But the sheer power of Smalltalk, the language, and the encompassing environment makes it, at the very least, incredibly intriguing.

As for implementations, for hobbyists, the most commonly used environment is Squeak, or it’s more professional cousin Pharo. I’ve settled on the latter, as it seems to be taking a more professional tack, but it’s really a matter of preference.

By the way, what I’ve said isn’t actually true of GNU Smalltalk, but having never used it, I can’t really speak to it’s viability as a platform. Of course, feel free to take a look at it and let me know what you think!

#### Where Were We

Oh yeah. Enter Seaside.

So what’s Seaside? Well, it provides an advanced web development framework for Smalltalk that allows the developer to just, you know, get on with it already.

Yeah yeah, I know, you’ve heard that before. So let me illustrate an example for you, and perhaps you’ll see why Seaside excites me so much.

#### The Example

The program we want to develop is incredibly simple:

1. It presents a counter to the user.
2. It presents a “decrease” link which lowers the counter.
3. It presents an “increase” link which increases the counter.

That’s it. Now imagine, in a traditional web framework, how you would do this. Well, obviously, you need some amount of state, here, in order to track the counter. You could squirrel the value away in a hidden field in a page form (seriously ugly). Or you could assign the user some kind of session ID, and then track the state on the server, using that session ID as a reference (somewhat complicated). Either way, you, the developer, have to focus on how, exactly, that state will be managed.

Now let’s look at how this program would be expressed in Seaside. First, a class declaration:

WAComponent subclass: #Counter
instanceVariableNames: 'count'
classVariableNames: ''
poolDictionaries: ''
category: 'Counter'


This is a simple class declaration describing a subclass of WAComponent named Counter, and containing an instance variable called ‘count’. Okay, so now we need an initializer:

Counter>>initialize

super initialize.

count := 0.


Again, nothing too special here, we just want to initialize our superclass and our counter. But now comes the meat of the program, and the magic:

Counter>>renderContentOn: html

html anchor
callback: [ counter := counter + 1 ];
with: 'increase'.

html space.

html anchor
callback: [ counter := counter - 1 ];
with: 'decrease'.


Voila, that’s the entire application, including links and state management.

No, really, that’s it. The whole thing.

So, how does it work? Well, first…

#### A Bit On Blocks

Like other high-level languages such as Perl, C#, and others, Smalltalk supports the concept of a closure, which is called a block, encapsulating a chunk of code along with it’s lexical scope. That code can then later be invoked at your leisure. For example:

| var block |

var := 5.

block := [ Transcript show: 'Hello world, my value is '; show: var; cr ].


The variable ‘block’ now contains a reference to a closure which we can then invoke later with:

block value.


This block remembers everything in it’s lexical scope, so, for example, the variable ‘var’ will retain it’s value, 5, and be emitted on the transcript. This fact, that closures are stateful code objects, is key to the way Seaside works.

#### Back To The Example

So, in Seaside, you never hand-write HTML. There aren’t even any templating languages. You generate all your HTML with code.

Yes, I know, this is weird, but bear with me.

You see, this has a major advantage. Consider the following piece of code from the example:

html anchor
callback: [ counter := counter + 1 ];
with: 'increase'.


Of course, this spits out an anchor. Nothing fancy there. But notice how we didn’t specify a URL? That’s weird enough. But notice something else? There’s an argument called ‘callback’, and we’re providing it a block of code. Can you guess what’s happening here?

That’s right. Under the covers, Seaside generates a URL for us. When the link is clicked, Seaside invokes the callback automatically. And because the block remembers the lexical scope, it can fiddle with the counter variable, incrementing it.

So because we let Seaside generate the HTML, suddenly our program is incredibly simple. Under the covers, Seaside manages all our state for us, associating an instance of the Counter object with our browser session. When those links are clicked, the callbacks are invoked in the context of that Counter instance and can manipulate the state of the system. Suddenly we’re no longer hacking HTML, parsing CGI parameters, and all that hideous garbage. We simply write what we want (‘when the user clicks this link, increment the counter’), and Seaside does the rest.

#### Conclusion

So there you go. A really quick intro to Smalltalk and Seaside. As you can tell, this is incredibly exciting to me. Why? Well, developing web applications has always struck me as incredibly tedious. Rather than just being able to write my damn application, I’m stuck parsing query parameters, managing state, manually handling state transitions, and a whole bunch of other garbage that’s really only peripheral to the actual act of building an application. Seaside, on the other hand, gets rid of all that tedium and lets me focus on the important thing: building a powerful application.

And note, I’ve only just scratched the surface here. Among Seaside’s other powerful features, it has cleanly integrated:

1. JQuery
2. Prototype
3. Scriptaculous
4. A general AJAX framework for doing partial page updates
5. And probably a whole bunch of other stuff.

Mighty cool if you ask me.

So, all this said, again, the picture isn’t completely rosy. As with all things, there are many issues that Seaside developers must face:

1. Myriad persistence solutions that are of mixed quality.
2. Code management issues.
3. Deployment issues.
4. Scaling and performance challenges.

And probably other stuff, too. Which will, of course, be fodder for further posts on this topic.