- AmbientTalk is a scripting language for Android devices designed to be robust against disconnections through asynchronous and peer-to-peer communication (P2P). - It allows for discovery of other devices for collaboration, and buffers communication when connections are down. - The presenter demonstrated a collaborative drawing app built in AmbientTalk that required only 90 lines of code to handle the networking, showing the ease of building P2P mobile apps with the language.

1. AmbientTalk:
A scripting language
for Android devices
Dries Harnie
Tuesday 25 January 2011
Hello everyone, my name is Dries Harnie and I’m here to present AmbientTalk: a scripting
language for android devices.

2. The AmbientTalk Team
Wolfgang De Meuter Tom Van Cutsem Stijn Mostinckx Elisa Gonzalez Boix Dries Harnie
Andoni Lombide Christophe Scholliers Eline Phillips Kevin Pinte Lode Hoste
Tuesday 25 January 2011
We are AmbientTalk. Resistance is futile.
Look for us with the ambientTalk tshirts

3. Motivation
Tuesday 25 January 2011
As discussed by the panel.

4. “Put everything in the cloud”
What is wrong with this picture?
Tuesday 25 January 2011
cloud printing.
Who here has ever printed when he was not in walking range of a printer?
You want to walk up to a printer and say “print this”, not find it in a cloud and then print to it
over a slow connection.

5. A very cool cloud app.
Tuesday 25 January 2011
This is a service I joined recently.
They allow you to store files in the cloud.
However, they do things differently.
If you have two devices on the same network, they will communicate directly, saving
bandwidth.
This is something we should embrace in ALL applications: why go via the cloud if you can do
it directly?

6. Goal
Tuesday 25 January 2011
We want to write an app that allows people to collaborate on some task (ie. painting).

7. AmbientTalk
- Asynchronous
- Peer to peer
Tuesday 25 January 2011
AmbientTalk!
Language designed to be robust against disconnections

8. Async. communication
Buffer when other side is down
Tuesday 25 January 2011

9. Discovery
“Sniffing around”
for other devices
Tuesday 25 January 2011

10. Deployment on real devices
Tuesday 25 January 2011
Because we wrote the AT interpreter in Java it runs unmodified on all desktop platforms.
We managed to squeeze it onto HTC Touch Cruise phones running the IBM J9 VM, but we ran
into all sorts of issues.
iPhone .. no real java support
Finally android, but not without issues.

11. Portability
issues: ✉
✓
Multicast ✓
- Works in 1.0
- Broken in 1.5
✗
- Fixed in 1.6
Tuesday 25 January 2011

12. Portability issues:
memory
AmbientTalk parser uses a lot of stack space
Many threads ... ++ungood.
Tuesday 25 January 2011

13. Portability issues:
serialization
ClassCastException: serialVersionUid doesn’t match
Three different classloaders
A) ClassLoader.getSystemClassLoader()
B) Thread.setContextClassLoader()
C) Foo.class.getClassLoader()
# This is the only one that knows about your classes.
Tuesday 25 January 2011
When transferring objects from/to android, make sure the serialVersionUid fields match.
These are usually computed, but dalvik and sun jvms do it differently.

14. The proof of the pudding...
http://youtu.be/k0HYqRCxtHc
Tuesday 25 January 2011
this is a demo we made yesterday.
I wrote the app in four hours.
~ 90 lines of ambienttalk, of which only 20 networking.
400 lines of java. mostly stolen from api demo.

15. import /.demo.weScribble
deftype Painter; def remoteInterface := object: {
def touchStart(other, x, y, color) {
def otherPainters := []; ... drawing stuff ...
};
whenever: Painter discovered: { |ref| def touchEnd(other, x, y) {
Android.Log.v("Fingerpaint", ... drawing stuff ...
"Discovered other painter:" + ref); };
otherPainters := otherPainters + [ref]; def erase() {
}; ... drawing stuff ...
};
network.online; };
export: remoteInterface as: Painter;
Tuesday 25 January 2011
I’ll even show you the code!
Look, an import statement ;)

16. Conclusion
@ambienttalk
http://ambienttalk.googlecode.com
Tuesday 25 January 2011