techno.blog("Dion")

My family has Macbooks solely. iPhones abound. We are an Apple family. I look around at work, at conferences, at the coffee shop…. and I see the same. Macs may be a small % of computers purchased, but they are an important percentage.

I jumped from Windows with glee. Finally, I can be productive with my computer. Things just work. Unix is under the hood so I can tweak away. I enjoy my computer. All important stuff and well worth paying for the BMW of laptops.

My fanboyism is waning though. My feelings are becoming more complex. The white/black of Apple/Microsoft has finally gotten the nuance of grey/grey. Whatever you say about BillG/Microsoft can you truly say that Jobs/Apple would have done any better in the “monopolistic” stakes?

It seems that with Apple doing well quarter over quarter we may get to see… via the iPhone. I am incredibly torn here. I love the iPhone, and it has changed the world of mobile. It feels like every year at JavaOne, someone would shout “mobile is here!” yet J2ME never brought it. No one did to the same extent as the iPhone.

Corporations are not intrinsically evil. Their goal is to create share holder value. There are various paths to this goal, and that is where it gets delicate… but I don’t think of corporates as evil. Making money is a good thing. Watching the ebb and flow of the business models on the Web and in software itself…. I am always looking out for where the business models are. Many long for the “good old days” of software. The simple days where you create something of value, and people pay money for that value directly to you. We went through shareware and freemium and ads. Others shout from the side line claiming that people will still pay for value! So, although I think keeping the core infrastructure of the Web open is vital (hence working at Mozilla!) I don’t think that everything should be open source and free.

I am getting a little worried about the mobile Web and the future of services and platforms. I think that users should be free to run their applications where they wish, and should control their data.

With the iPhone the platform is incredibly locked down. You basically have to use their tools, and built applications using a Mac. Then you get to send your application up to the Apple gods (reviewers) and if you are lucky, an end user can run your code. Unfortunately this process is cryptic and poorly implemented right now.

Apple can make a case that this process helps “keep us safe” (make sure apps do no evil) and “makes sure the store isn’t swamped by crap” (however there are a ton of crap apps!). I think that we should trust users and they should be able to install whatever they bloody want too. Apple should have a system that propagates known malware. A way for users to crowd-source issues just like Semantec is working on. As a developer I really have to wonder when I know that I could spend a lot of time on an application that a random Apple chap could block and thus wouldn’t see the light of day. No thanks!

Time to take a pill?

I am starting to feel ready to take the blue pill. To take it perhaps a little far, Apple has enslaved me by giving me yummy food (great hardware and software). It tastes so good, that I eat it and say “thank you sir, can I have another!”

I am picking on Apple a little here because it relates most closely to me, and the iPhone is exploding. I see how they are tying the block anyone out from iTunes and lock me in to their world. The world that Steve wants for us. Sorry Steve, but I am getting close to jumping from your utopia to create a better one, even if it doesn’t smell so nice.

The future has other fish to fry. As we think forward to a world without single devices, but instead with everything being a connected embeddable systems… maybe right in your clothes. In this world the battle will be for data and services. Who owns your data. Are the business models transparent? I have a funny feeling that we will have to constantly fight for this. Corporations don’t care, but people should, and some do.

I have always had this in the back of my mind with Apple. I didn’t jump all the way in. I kept my music apart from iTunes AAC lock and structure even though it was against convenience.

One side of my brain wants to continue. Take the red pill and enjoy a productive happy life. The rest of my mind is contemplating taking the blue pill. Maybe it will be ready with an advanced open web platform on the phone, one on the desktop, and eventually….. everywhere.

Is anyone else having these thoughts?

Do you sometimes feel like the browser is a black box? We are building richer and richer applications on the Web platform and this means that developers are running up against new issues to debug and test.

We feel like it is a great time to develop new tools that afford you the ability to look into the runtime to hopefully help you find a bug, or allow you to keep your application as responsive as possible.

Today we want to start a conversation about some of our thinking, with the hope that you will join in.

We have been taking a hard look at the tools landscape, and here is a presentation that gives you an idea of our thinking:

We will be posting more of our thoughts, but as you can hear, our vision for these tools is that they:

• Are able to run out-of-process. We view out of process tools as the preferred way to observe the runtime because it enables us to somewhat ignore the Heisenberg uncertainty principle. If we are profiler the browser, having to deal with NOT profiling the profiler code can be painful. Also, we want to be able to use the same tools on devices. I would much rather point my desktop tool to a Fennec device, compared to trying to use the tool on the phone itself! This leads us too…
• Enable cross browser experiences: Our lab doesn’t have the resources to develop deep integrations with multiple browsers, but we very much want to enable that. Since we are running out-of-process, we can document the communication API and many hosts can then be wired up.

The first experiment in this vein is a stand-alone memory tool prototype that lets you poke around in the JavaScript heap. What objects are there? How many of them are there? Any dangling references due to closures or event listeners?

To kick this off we worked with awesome Mozilla colleagues such as David Barron and Atul Varma which enabled us to spike down to the bare metal of the browser.

We ended up with an architecture for the tool that contains these components:

Firefox Add-on

A special Firefox add-on installs a binary component that gives us access to the low level JavaScript heap. This gives us a simple API with methods that allow you to enable profiling, get the root objects in the heap, and get detailed information on the objects themselves.

Firefox Memory Server

The current consumer of the core API is a min server. Once activated, the browser freezes and your only option to interact with it is via this server. It exposes a simple socket API with URLs mapping to the high level APIs. For example, you can access /gc-roots to get the root object ids. Or you can ask for details on an object via /objects/XXX where XXX is the object id you are inspecting. When you are done, you access /quit and the browser is unfrozen.

All of these APIs support JSONP which is how we get the data back into our main application.

NOTE: Currently, the server lives within the add-on itself (at chrome://jetpack/content/memory-profiler-server.html) but eventually this will migrated to a Jetpack.

Memory Tool Ajax Application

The main application itself is a simple Web application that can be run in any browser (not just Firefox!) After you have installed the Firefox Add-on, and turned on profiling via the Memory Server, you can visit the tool. Currently, after you connect, the tool gets a dump of the root object for the first tab in the browser (not including the memory server tab). You will see the meta data associated with the object, and you can click on any of the data elements that have their own memory id (memory locations are integers with 9 digits). This tree view lets you poke around the heap.

If you want to aggregate the data, you can click on the “2. Dump Heap” button, which goes through the entire heap (which can be big!) and aggregates all of the objects for you. If you see a massive number of objects of a particular type, this could be a flag!

Enough talk, lets see it briefly in action:

The tool is very early stage and changing constantly. However, it is all out in the open. You can grab the open source pieces:

• Firefox Add-on (currently includes memory server)
• Memory Tool Web App

As is always the case with Mozilla, and Mozilla Labs, we want to get ideas out into the community as soon as possible. This tool is very much alpha, and the goal of getting it out in the wild is to start a conversation about tools like these.

What tools in this area would help your job as a Web developer? We are all ears, and would like to share our dev tools mailing list / group as a good area to share ideas.

What about Firebug? This particular tool freezes the browser, and since Firebug is in-process right now, it wasn’t a great fit. However, we very much want to take this kind of work and get it into Firebug at some stage. We just aren’t at that stage yet!

On our side, we will be engaging with the Mozillans who truly grok the JavaScript (and entire browser) internals to see what interesting data we can expose to developers. We have found that the Firefox team has already added a lot of the infrastructure there, and now the task is to work out what will be useful, and how can we best report it.

We have plenty of ideas too. A wish list could contain:

• Short term clean up (fix the backend code that interfaces with the heap, abstract out the service into a Jetpack, and make sure we are using the correct APIs, and get these APIs added where appropriate)
• We want to visually add the graph to the object dump, so you can really understand what you are looking at. It will probably look something like this:

  

• We have wired up Bespin, and we will suck out the source code from functions and showing that inline to the tool itself. There is much more to do though, and we want to find out what you need.
• More profiling info: break up buckets of memory (images, js, DOM, etc)
• Great way to see who is reference whom (memory leak detection)
• Garbage Collection: When and how long are collections occuring?
• Granular filtered profiling: Profile this event and measure every event-of-interest from the start of navigation to the present e.g. DNS & TCP connections, page header parsing, resource fetching, DOM parsing, reflow, etc.
• Web Worker thread monitoring
• Have a profiling mode that gives you data without having to freaze the heap, and only when you need to do a deep dive do we get to that.

We have learned a lot as we created this prototype. Atul is going to write up his experience, and we will continue to talk in the open about how we take this prototype and your ideas to the next level with browsers.

Update

Atul has posted on his experience with SpiderMonkey and how the JS Runtime works. Nice in depth stuff. He also created PyMonkey “a Python C extension module to expose the Mozilla SpiderMonkey engine to Python.” which is crazy cool.

original by mwboeckmann

Everyone got in a tizzy over the Google very-early-darn-leaks-pre announcement of Chrome OS. There have been many attempts at a “launch into browser” system, and the timing / marketing hasn’t been right. The journalists have by and large shown that they do not understand any nuance and could only think to write about the external battle of the titans (Chrome OS to destroy Windows!) or the internal battle of the titans (Android vs. Chrome OS).

The news is so early, that it is mainly a no-op right now, other than showing that to get to that point, Chrome will probably be extended quite a bit (access to more native services etc). I am a believer that this has to happen (hence Gears fan), but I also do worry that it will be rushed. We don’t want to fork the Web….. but let’s wait and see.

What I find most interesting though, is that I don’t think that the world needs a computer that boots almost-solely into a browser.

Kent Beck was talking about how he is using Chrome Browser OS right now as a social experiment. Yes. We can all delete every application from our machines and maximize a browser and live in it. That isn’t what will be exciting about a true Web platform.

I have been playing with a Windows laptop, and what has interested me is how much I can get done because my world is available through the browser. Back in the day, if I was at a friends house, I would download putty.exe and telnet/ssh into my world, and it would be ugly text. Now, I can jump on a random computer and access my entire social environment (email, twitter, etc). I can get real work done. One of the reasons that we did Bespin was to extend that to coding too.
This brings me to my benchmark for when I think a web OS will be here.

If I can sidle up to a random computer and have access to everything that I can do on my own laptop, then we have made it

Ironically, I almost used to be able to do just that! In university I could login to any machine on campus and see my screen exactly as I left it. I want X back baybee! ;)

We are getting closer, yet still a ways off. I hate the management that I have to do with iTunes. I want to by the license to play music, and have my collection in the cloud, and sync’d in smart ways. I want to be able to set profiles for what is downloaded and offline-available on my laptop versus the media server vs. the ball and chain’s laptop vs. my phone.

I want my settings to follow me around. Another reason why I am so excited about the future of Weave-like services. Let me login to the browser and get my history, passwords, awesomebar setup for me. Go further, and let me “switch user” on the persons machine and have the login be an identity service like Open ID, Facebook, Weave, or what have you.

When we have an open identity system that works, with services that let you take your entire world with you hooked to your identity, then we can talk about how cool the Web platform is as an OS. We will have moved up the services stack from managing the state of windows on the screen, to higher level services.

Marry this to auto syncing of data between all of your devices, and you have a truly new world. Give me that world, not just and autoexec.bat that launches browser.exe :)

As I think about a lot of the features that excite me the most about Bespin, they tend to break up into features that connect people, and those that add more dimensions to the software development process.

Doing more with Time

When I look at the evolution of editors, we have been mostly stuck looking a files, with the odd perspective on top of that (e.g. show me class diagrams). We have used tools like VCS to be able to go to different points in time, but I haven’t seen a popular editor that does much more than that.

One feature that I am excited about in Bespin, is the ability to have a “time machine” construct. I want to be able to flip around in time and see the code change before my eyes. On the timeline, I should be able data points such as: when commits happened, issues that track to the code, code size, who worked on it, etc.

I would also use this feature a lot casually. For example, to view a new commit that came in, I could simulate walking through what the developer did with that patch and grok it inline instead of staring at a huge diff. When you add the dimension of time to the tool in a deep way, I think developers will be able to add a lot of interesting features to help them visualize and produce great code.

Find Usages++

I wish I had better pivot tables for my code. We often make choices on how we compose our code modules, and there are always tradeoffs. Do you put your cross cutting concerns into the objects so when you look at one object you see it all? Or do you put the same things in a separate area so you can see “all the times I do X”. We run into this issue in spades with meta programming, where it can be hard to see everything that is going on.

Rather than having to make a choice, I want to pivot my code on the fly. I want to be able to ask my code:

• Show me all of the data access logic that is used in this app
• What are all of the URL mappings
• Where is all of the keyboard handling
• What are all of the public events that I could hook into?
• What are all of the consumers of the event “foo”

I am interested to see if there is a way to easily get at my code in new ways, and also be able to make changes and have those changes go back to the right place. This is tricky…. but intrigues me.

Heuristics

Why am I not being told more about my code? It feels like I have to poll my tools all the time, and they don’t tell me much. Granted, I get help with syntax checking, incremental compilation, completion… great stuff. But, I want more.

I want to be told when I am duplicating a bit of code. I want to be told the instant I cause a regression in some tests. I want to be told the minute something I do messes up in a runtime (e.g. a browser). I want to be told the minute another developer on the team stepped on the same code (commit so she has to merge!).

There are a ton of heuristics that we can do on the client and up in the cloud (aside: fun little jap on cloud “#chromeos reinforces my belief that cloud computing is just mainframes with rounded corners.”)

This isn’t just about code, but also about the project lifecycle too. I need to write a separate post on that, and what is doing in that area.

Visualizations

I just happened across Code Canvas, a prototype zoomable UI for looking at a code project.

It is exciting to get time to think in the developer tools space. There is just SO MUCH that can be done to make development more fun and productive. By adding in low level hooks to multiple dimensions, I hope that we can do a lot more. What would you like to see?

We are having a great time using Canvas for Bespin and a few other projects. Having text, images, and boxes as the primitives on the Web just isn’t good enough, so leap frogging to HTML5-land where we have the ability to arbitrarily paint pixels is fantastic. Mix this with the ability to directly manipulate video, and you have new opportunities.

However, Canvas also has obvious issues. How do you make it accessible? Or searchable? We have some ideas there, but they are a long way off. The goal has never been to use Canvas as the shiny toy. With Bespin, we actually tried to do it with DOM, and it wasn’t so much chutzpah as “can’t get it to perform”-pah that lead us down the path of Canvas. The usual suspects in the stack weren’t working for us, whereas others were blazing (e.g. JavaScript performance has blown us away, as has Canvas itself).

With major browsers like Firefox 3.5 (Safari 4, Chrome 2, etc) I am very much excited to work with browsers (say, the great Firefox team :) to kick into gear on the next level of improvements. The current batch have been competing on the performance of JavaScript. The new engines are fantastic, and really change the game on what can be done. Add in Web Workers to the magnitude speed bump of JS and Web devs can truly build responsive low-latency applications. We are now seeing improvements to the DOM, the next frontier. It is all well and good to have your JS run nice and speedy, but if the DOM can’t keep up then we are still in trouble. This is why we had to go to Canvas for Bespin in the first place! I am hoping that we will be able to push on DOM and other APIs to get to a point where our DOM based Bespin can come back to town.

There is a time and a place for Canvas though. Rather than running the show, I much prefer the unobtrusive extensions that you can provide. I am also looking forward to seeing more tools that use a server side component to do some image manipulation… now work on the client through Canvas and ImageData. Vlad pondered why CSS spriting tools are all server-side for example.

Christian Effenberger has been doing this kind of work for a long time, and there is room for a lot more. I really like having Canvas available in more places, such as anywhere an image can be used (e.g. WebKit CSS extensions where you can use a Canvas as a background-image). That gives you full control to style something in zany ways, while still staying in DOM land. It also means that things can play together really nice. We continue to push more into CSS (transitions, gradients, etc.) and animation libraries (Scripty2 looks nice!).

There is still much work to be done on putting the pieces together. I don’t know about you, but doing some common things with layout and UI still drive me nuts. Having the low level new tools like border-image are cool, but I really long for a tool that graphically lets me take a mock, cut it up, and build it out as a generalized component (stretches in the right place etc). The tool could then spit out more than just a border-image version, but old style divs + CSS to make it work everywhere. One tool, run output anywhere.

So, time to take a breath, take a look at what bleeding edge folk are doing to get rich experiences, and push it into the core platform itself. This will mean less Canvas, but used in the right places, and we will move down the stack again. If we don’t push use cases down into the core, then we are doomed to stagnate or fork the Web.

Imagine this scenario. Say you worked for a company that had a top website and a new browser came out. There were some known bugs when said browser used your website, so you would obviously change the website ASAP. Chance are that you are ahead of the game and already had the fixes ready as you tested with release candidates. Your users grab the latest and greatest browser and use your website with glee.

Now imagine if the following happened: the browser vendor was in charge of your website and you had to ask nee plea with it to update your site. The vendor refuses at first and you have no control at all! All of the users that have upgraded their browser are now getting a sub-par experience. It’s your site, but you have no control. You curse as you know that the fix is RIGHT FRIGGIN THERE but hasn’t been applied.

This is crazy talk. You would never cede control like that. But wait, isn’t that what can happen with the iPhone and Apple? Facebook is one of the most popular applications on the iPhone, yet I read the following from poor Joe Hewitt, the guru that single-handedly created Facebook for iPhone, as well as the original Firebug, worked on Firefox, and much much more:

Submitted an update to the Facebook app a few weeks ago to fix OS 3.0 issues, still awaiting approval.

As of right now, if I am running Facebook on the iPhone 3Gs there are known bugs that Joe has fixed. I can’t run it. This is how they treat THEIR TOP APPLICATIONS which has a brand name company behind it? Imagine how they treat the poor lowly buggers on the totem pole.

Well, actually, we don’t really have to wonder too much. How gutted are you if you bet a year of your company on something with some amount of apparent blessing from Apple, and then see it thrown back in your face with some rule cited … when you know that the guy next door got his work in even though he is doing the same or worse!

Back to Joe. He got the latest 3Gs and talked about how smooth it is. This is great news. I feel like I often have a frozen UI on my 3G (typing, scrolling, any interaction) and it bugs me. If Apple has gotten their device “responsive enough” where the average user doesn’t notice these glitches, they have gone a long way, and as Joe mentions…. will give him time to work on features and not tweaking his code to try as hard as possible to keep his UI responsive (which in some circumstances was proving impossible). Ben has told me “It’s like the PowerBook G4 to MacBook Pro upgrade dude” which is great to hear since recently all upgrades have felt like a wash (e.g. recent Macbook Pro upgrades).

Also, I took another look at the applications that I have installed on my phone, and quickly realized that I use ~5% of them. I have a huge number that I have probably run once. When I look at the ones that I do use, I also quickly saw that the vast majority could easily be web applications, especially with the HTML5 features of Mobile Safari. If Apple continue to open up the API to the WebView (or PhoneGap / Titanium Mobile continue to thrive) then it will be so easy to create a large swarth of applications using simple Web tech. Sure there will be reasons to go closer to the metal, but for a lot…. you won’t have to. That is exciting stuff. I would also love to chat more with Joe about his experience using Cocoa vs. Web tech for layout etc. We have chatted a little, but I would love to talk more.

I went back and forth on getting an upgrade this time around. I was a definite “No” at first due to the pricing, and then AT&T came out saying that they would be helping out, so Ben and I went to check it out. Note: we both were in the same line for the 3G last time around, and at the store we found out that HE got to get the phone for $200 (as a “valued customer”) whereas I would have the pleasure of paying $300 more. I couldn’t whip out my credit card and walk out with the same hardware as him for a shed load more. So, now he will get the chance to lord over me until I do make the upgrade “wow this compass is amazing. wow the responsiveness is fantastic. How did I live without video right in my pocket.” Or, maybe I will jump to a Pre and start hacking on the native SDK that is just Web itself?

It was cool to see the second release of Jetpack with its storage, slidebars, and time travel from the .future().

I quickly hacked up a trivial slidebar that lets me mouse to see the source of the current tab, and click on it to have it stick around. All in a few lines of code that use the new future API, slideBar, and tabs:

jetpack.future.import("slideBar");
 
jetpack.slideBar.append({
  url: "view-source:" + jetpack.tabs.focused.url,
  width: 500,
  onSelect: function(slide) slide({ size: 500 }),
  onReady: function(slide) $(slide.doc).click(function() {
    slide({ size: 500, persist: true });
  })
});

Check out the screencast too:

With a wife with a masters in education, you tend to think and chat about education from time to time. I enjoy thinking about how social software could help education in the future. One of the fields that I enjoy thinking about is Maths. It was my favorite subject as a kid and I had the benefit of a great teacher. In general though, it feels like Math is often taught in such a painful way.

I remember being sent an article that discussed how Math is taught by comparing it to music. It postulates a world in which music is taught without instruments. You have to learn music theory for 10 years before you get to pick up that flute. What kid would get excited about a world of that music? That is what we do to them with Math.

Time for Pie

I mentioned the Bespin pie menu before. In our first version you jump to the different pieces with the keyboard. Of course, one of the benefits of a pie menu is that Fittss’s Law kicks in and you can easily jump to an item. (Aside: the dirty secret of our pie menu is that it isn’t really a pie menu, it currently sits at the bottom and not where you right click etc.)

As we start to put in mouse support, the first thing we need to do is be able to determine which slice of the pie is being clicked on so we can activate it. This gave me the opportunity to go down trigonometry lane.

If the pie was sliced with vertical and horizontal lines like the image above, then it would be very simple indeed. To start with, what information do you get when the user clicks? We get an x and y coordinate with an origin starting point in the top left. There are various x and y coordinates that you will get from the MouseEvent (x, y, offsetX/Y, pageX/Y, rangeX/Y, clientX/Y, layerX/Y). We care about the offsetX/Y or layerX/Y value (depending on the browser), which will give us the point with the origin starting at the top left of the canvas itself and not the window.

With the example above you could simply take the computed x and y coordinates and simply check them to determine the segment. For example, if x is less than the radius then it is a segment on the left. If y is less than the radius then it is a segment on top.

But we don’t have that luxury. Instead we have to do some simple Math. I drew out the problem with various bits of information here:

You will see the slices match the pie menu, and I drew in an X and Y axis that cuts through the center of the pie. In the diagram you will see an “x” marking the click in the right slice. How do we work it out? Well, what do we know? First we can calculate the location of the point based on the center of the circle. Remember that the browser will tell you the x and y based on the top left and not the center, so we quickly repurpose the coordinate based on the top left of 390, 180 and convert it to 140, 70. This is simply done via:

function centerPoint(x, y) {
    return { x: x - RADIUS, y: (y - RADIUS) * -1 };
}

Now we have the relative point from the center of the circle we can calculate the angle that will then in turn let us know which quadrant we are in.

Arctan and atan2()

The easiest way to calculate which quadrant we are in is to simply calculate the angle of the dangle. To do that we calculate the arc tangent between two lines in a triangle, the y=0 line across the x axis, and a line between y=0 and the point in question.

It turns out that we get this calculation for free, via Math.atan2:

function angle(x, y) {
    return Math.atan2(y, x) * 180 / Math.PI;
}

To explain how this works, see the scribble below that shows 4 different points and the resulting angles based on angle(). One gotcha that you will notice is that atan2() takes the coordinates in the order: y, x but elsewhere you are used to using the opposite x and then y. Be careful!

Once we have the angle based on the x axis, we can have a simple case statement to check the bounds.

If the angle is below -45 and 45 degrees, it is on the right. Greater than 45 and less than 135? Then we have the top. And so on.

With a little fun Math, we get to have Pi solve our Pie problem. To see the code at work, check out the test bed.

Ben and I both got new work 15″ Macbook Pro laptops, and Ben isn’t happy.

I have to admit that it doesn’t feel like the Apple designers may have gone one step too far with the trackpad. In one fell-swoop they took away the button and added new and exciting gestures.

The big problem I have with this is that I have learned to use the trackpad with one thumb at the bottom (where the button was) and I use my index finger to move around. There is a lot of muscle memory there. What this means in practice is that I am in Gmail and the pinch gesture kicks in which results in my font changing size, or the rotate gesture causes an image to skew in Keynote.

In theory, it is beautiful to get rid of the button. In practice I miss the tactile feedback, and the separation of concerns.

Maybe I should quickly grab a Macbook Air which still has the small little trim mouse button?

To those at you who have been using the latest generation of Macbooks, do you get over this? Will this be something that I forget in a month and life will actually be better?

Rich Hickey (Clojure creator) gave one of the best talks that I have been in for awhile. The title of the talk was scarily low level and “wow this must be boring”-y, but the title should have been something like “Learn about how the real world works”.

The first part of the talk discussed philosophy and how our software is totally messed up due to us not taking the factor of time into account properly. So many functional programming talks go into the bizarreness of Monad details and the like, in a way that makes a non-Functional chap’s head blow up.

Rich on the other hand didn’t go there. No need to say “Monads are in Haskell as an escape hatch past the whole state issue”. Instead he discussed the general notion of time and how it relates to variables. Short version: variables are variable in that they change over time, so really we want immutable values with different ones at different points. He talked about the different notions of time (before, at the same time, after, now, etc) and how the concurrency / thread problems become a touch more obvious when you think about things in that way.

And it went on from here. He talked about the great design of the data structures in Clojure and how they almost always uses a nice multiple version control system that enables a lot of things to “just work” in a concurrent and safe way. And of course, you have to have a little bit of fun with the Java Data API and how you can do things like someDate.setMonth().

This is the kind of talk that will make you think differently about your code, even if you are not in functional world. You will think about taking value snapshots to work with instead of passing around quite so many references. It was highly entertaining and will have me thinking for quite some time.

Related Interview: Rich Hickey on Clojure’s Features and Implementation

In this interview taped at QCon London 2009, Rich Hickey talks about all things Clojure: Software Transactional Memory, concurrency, persistent data structures, ports, AOT compilation, and more.