AAML - another android markup language

Sometimes I do android apps development. I use terminal, tmux and vim - no Eclipse, no IntelliJ Idea or other IDEs.

What I don’t like in android development is XMLs. It’s a lot of typing, and I don’t like to type a lot. So, here’s my attempt to make it easier for those who use minimal tools for android development. Maybe it would work for Eclipse, too.

Goals

Simple syntax: minimal punctuation, no closing tags
Should suit for most XMLs: layouts, values, strings etc.
Should have macros support to extend language and to define variables
Should work on Linux, Macs and probably Windows

Example

A piece of code paints a thousand words.

Here’s AAML markup you edit manually:

:LinearLayout layout fill, padding 0dp 16dp, orientation vertical
        :EditText
                layout fill wrap
                hint @string/to
        :EditText
                layout fill wrap
                hint @string/subject
        :EditText
                layout fill 0dp 1
                gravity top
                hint @string/message
        :Button#btn_send
                layout 100dp wrap
                gravity right
                text @string/send

And here’s what you get after converting it to XML:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:paddingTop="0"
        android:paddingBottom="0"
        android:paddingLeft="16dp"
        android:paddingRight="16dp"
        android:orientation="vertical">
        <EditText
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:hint="@string/to" />
        <EditText
                android:layout_width="fill_parent"
                android:layout_height="wrap_content"
                android:hint="@string/subject" />
        <EditText
                android:layout_width="fill_parent"
                android:layout_height="0dp"
                android:layout_weight="1"
                android:gravity="top"
                android:hint="@string/message" />
        <Button
                android:id="@+id/btn_send"
                android:layout_width="100dp"
                android:layout_height="wrap_content"
                android:gravity="right"
                android:text="@string/send" />
</LinearLayout>

Sounds easy, right?

Implementation

I’ve picked Python 3 to write AAML converter (though with python2 it seems to be working, too). Basically, AAML has three parts: reader, processor and writer.

Reader is simple: everything that starts with a colon is a new element. Indentation level allows to nest elements. Next, element attributes are comma separated and comma is automatically inserted after the end-of-line. Normally the first word in the element is tag name, you should not use newline or comma to separate it form the element attributes. That’s the whole syntax of AAML.

Writer is simple, too. It just pretty-prints all elements.

Processor expands aliases and macros.

Alias is a single word that is substituted by another word. Useful for defining variables.

Macro is a bit more complex. It has a name and a list of arguments. When expanded, first all arguments are expanded (if they are aliases), then a suitable macro is looked up in the environment and processed.

Here’s how it looks like. To define a macro use def tag (yeah, def is a keyword, you can’t make an XML element called def). Then you write macro name and a number of arguments it supports. Macros can be overloaded, but no support for variable number of parameters so far. Then you write macro body. You can refer to macro parameters as positional arguments, e.g. $1, $2 etc. Here’s an example of some layout macros:

# Aliases
:def fill fill_parent
:def wrap match_parent
:def match wrap
# Macros
:def layout:3 layout_width $1, layout_height $2, layout_weight $3
:def layout:2 layout_width $1, layout_height $2
:def layout:1 layout $1 $1

:TextView
    layout fill
:TextView
    layout fill match
:TextView
    layout fill match 1

There are two more things to mention. Comments are allowed, but should take a separate line and start with #. Also, as you use android:id frequently, you can use syntax sugar like TextView#my_text to define a new id my_text (as an alternative to TextView id "@+id/my_text").

Usage

You can get the sources at https://bitbucket.org/zserge/aaml. You need Python to run it. No other dependencies required. If you use Vim there is also a tiny syntax highlighting script included (see aaml.vim).

You can process either files or directories, like:

# Read from stdin and write to stdout
$ aaml - -
# Convert one file
$ aaml my_layout.aaml my_layout.xml
# Convert all *.aaml files from directory aaml to *.xml files 
# in the directory res
$ aaml aaml res

You can always use custom_rules.xml to build XMLs from aaml files automatically with ant debug or ant release:

<?xml version="1.0" encoding="UTF-8"?>
<project>
    <target name="-pre-build">
        <exec executable="aaml">
            <arg value="aaml"/>
            <arg value="res"/>
        </exec>
    </target>
</project>

No need to say that it’s pretty much unstable yet and has issues. So, you are welcome to report them.

Volunteers needed to add more syntax highlighting modules for Sublime Text, Emacs and other popular editors, to suggest standard macros for android development and to do testing.

AAML is free software and distributed under MIT license.

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Apr 02, 2013