Hello world in Scheme for Android

(Here is the latest version. This is in turn an update of the original version.)

Google's phone operating system "Android" is based on a custom Java virtual machine on top of GNU/Linux. So it occurred to me: How difficult would it be to get a Kawa application running on Android? Not that difficult, it turns out.

Here is "Hello world" written in Kawa Scheme:

(require 'android-defs)
(activity hello
   (let ((tv (android.widget.TextView (this))))
     (tv:setText "Hello, Android from Kawa Scheme!")

The following instructions have been tested on GNU/Linux, specifically Fedora 10, but if you've managed to build Android applications under (say) Windows, you should be able to appropriately modify these instructions. The article Android Phone development from the Linux command-line helped me figure out what to do.

Getting and building Kawa and Android

First download the Android SDK. Unzip in a suitable location, which we'll refer to as ANDROID_HOME.

$ ANDROID_HOME=/path/to/android-sdk-linux_x86-1.0_r2

To get things to work I had to make some modest changes to Kawa, so you will need to get the Kawa developer sources from SVN.

You need to configure and make Kawa appropriately:

$ KAWA_DIR=path_to_Kawa_sources
$ cd $KAWA_DIR
$ ./configure --with-android=$ANDROID_HOME/android.jar --disable-xquery
$ make

Creating the application

Next, we need to create a project or activity, in the target directory KawaHello, with the main activity being a class named hello in a package kawa.android:

$ activitycreator --out KawaHello kawa.android.hello

Replace the skeleton hello.java by the Scheme code at the top of this note:

$ cd KawaHello
$ cd $HELLO_APP_DIR/src/kawa/android/
$ rm hello.java
$ emacs hello.scm

We need to copy/link the Kawa jar file so the Android SDK can find it:

$ ln -s $KAWA_DIR/kawa-1.9.3.jar libs/kawa.jar

We also need to modify the Ant build.xml so it knows how to compile Scheme code:

$ patch < build-xml-patch.txt

Finally, we can compile our application:

$ ant

Running the application on the Android emulator

Start up the Android emulator:

$ emulator&

Wait until Android has finished booting, clisk the menu and home buttons. Click the tab above the menu key to show the installed applications. Now install our new application:

adb install bin/hello-debug.apk

The new hello application should show up. Click it, and you should see something like: HelloKawa1.png

Running the application on the G1 phone

If the emulator is running, kill it:

$ kill %emulator

Connect the phone to your computer with the USB cable. Verify that the phone is accessible to adb:

$ adb devices
List of devices attached 
HT849GZ17337	device

If you don't see a device listed, it may be permission problem. You can figure out which device corresponds to the phone by doing:

$ ls -l /dev/bus/usb/*
total 0
crw-rw-rw- 1 root wheel 189, 5 2009-01-18 16:52 006

The timestamp corresponds to when you connected the phone. Make it readable:

$ sudo chmod a+w /dev/bus/usb/001/006

Obviously if you spend time developing for an Androd phone you'll want to automate this process; this link or this link may be helpful.

Anyway, once adb can talk to the phone, you install in the same way as before:

adb install bin/hello-debug.apk

Some debugging notes

You will find a copy of the SDK documentation in $ANDROID_HOME/docs/documentation.html.

If the emulator complains that your application has stopped unexpectedly, do:

$ adb logcat

This shows log messages, stack traces, output from the Log.i logging method, and other useful information. (You can alternatively start ddms (Dalvik Debug Monitor Service), click on the kawa.android line in the top-left sub-window to select it, then from the Device menu select Run logcat....)

To uninstall your application, do:

$ adb uninstall kawa.android