The Asterisk Extension Language
===================================

Over time, people have been pushing to add features to extensions.conf to make
it more like a programming language.  AEL is intended to provide an actual
programming language that can be used to write an Asterisk dialplan.

Getting Started
-------------------------
The AEL parser (pbx_ael.so) is completely separate from the module
that parses extensions.conf (pbx_config.so).  To use AEL, the only thing that
has to be done is the module pbx_ael.so must be loaded by Asterisk.  This will
be done automatically if using 'autoload=yes' in /etc/asterisk/modules.conf.
When the module is loaded, it will look for 'extensions.ael' in /etc/asterisk/.
Both extensions.conf and extensions.ael can be used in conjunction with each 
other if that is what is desired.  Some users may want to keep extensions.conf
for the features that are configured in the 'general' section of 
extensions.conf.


Reloading extensions.ael
-------------------------
To reload extensions.ael, the following command can be issued at the CLI.

	*CLI> reload pbx_ael.so


Contexts
-------------------------
Contexts in AEL represent a set of extensions in the same way that they do
in extensions.conf.

context default {

};


Extensions
-------------------------
To specify an extension in a context, the following syntax is used.  If more
than one application is be called in an extension, they can be listed in order
inside of a block.

context default {
	1234 => Playback(tt-monkeys);
	8000 => {
		NoOp(one);
		NoOp(two);
		NoOp(three);
	};
	_5XXX => NoOp(it's a pattern!);
};


Includes
-------------------------
Contexts can be included in other contexts.  All included contexts are listed
within a single block.

context default {
	includes {
		local;
		longdistance;
		international;
	};
};


Dialplan Switches
-------------------------
Switches are listed in their own block within a context.

context default {
	switches {
		DUNDi/e164;
		IAX2/box5;
	};
	eswitches {
		IAX2/context@${CURSERVER};
	};
};


Ignorepat
-------------------------
ignorepat can be used to instruct channel drivers to not cancel dialtone upon
receipt of a particular pattern.  The most commonly used example is '9'.

context outgoing {
	ignorepat => 9;
};


Variables
-------------------------
Variables in Asterisk do not have a type, so to define a variable, it just has
to be specified with a value.

Global variables are set in their own block.

globals {
	CONSOLE=Console/dsp;
	TRUNK=Zap/g2;
};

Variables can be set within extensions as well.

context foo {
	555 => {
		x=5;
		y=blah;
		NoOp(x is ${x} and y is ${y} !);
	};
};

Writing to a dialplan function is treated the same as writing to a variable.

context blah {
	s => {
		CALLERID(name)=ChickenMan;
		NoOp(My name is ${CALLERID(name)} !);
	};
}; 


Loops
-------------------------
AEL has implementations of 'for' and 'while' loops.

context loops {
	1 => {
		for (x=0; ${x} < 3; x=${x} + 1) {
			Verbose(x is ${x} !);
		};
	};
	2 => {
		y=10;
		while (${y} >= 0) {
			Verbose(y is ${y} !);
			y=${y}-1;
		};
	};
};


Conditionals
-------------------------
AEL supports if and switch statements.  Note that if you have an else 
clause, you MUST place braces around the non-else portion of the if 
statement.

context conditional {
	_8XXX => {
		Dial(SIP/${EXTEN});
		if (${DIALSTATUS} = "BUSY") {
			Voicemail(${EXTEN}|b);
		} else
			Voicemail(${EXTEN}|u);
	};
	_777X => {
		switch (${EXTEN}) {
			case 7771:
				NoOp(You called 7771!);
				break;
			case 7772:
				NoOp(You called 7772!);
				break;
			case 7773:
				NoOp(You called 7773!);
				// fall through
			default:
				NoOp(In the default clause!);
		};
	};
};


goto and labels
-------------------------
This is an example of how to do a goto in AEL.

context gotoexample {
	s => {
begin:
		NoOp(Infinite Loop!  yay!);
		Wait(1);
		goto begin;
	};
};


Macros
-------------------------
A macro is defined in its own block like this.  The arguments to the macro are
specified with the name of the macro.  They are then reffered to by that same
name.  A catch block can be specified to catch special extensions.

macro std-exten( ext , dev ) {
        Dial(${dev}/${ext},20);
        switch(${DIALSTATUS) {
        case BUSY:
                Voicemail(b${ext});
                break;
        default:
                Voicemail(u${ext});
        };
        catch a {
                VoiceMailMain(${ext});
                return;
        };
};

A macro is then called by preceeding the macro name with an ampersand.

context example {
	_5XXX => &std-exten(${EXTEN}, "IAX2");
};


Examples
------------------------

context demo {
	s => {
		Wait(1);
		Answer();
		TIMEOUT(digit)=5;
		TIMEOUT(response)=10;
restart:
		Background(demo-congrats);
instructions:
		for (x=0; ${x} < 3; x=${x} + 1) {
			Background(demo-instruct);
			WaitExten();
		};
	};
	2 => {
		Background(demo-moreinfo);
		goto s|instructions;
	};
	3 => {
		LANGUAGE()=fr;
		goto s|restart;
	};
	500 => {
		Playback(demo-abouttotry);
		Dial(IAX2/guest@misery.digium.com);
		Playback(demo-nogo);
		goto s|instructions;
	};
	600 => {
		Playback(demo-echotest);
		Echo();
		Playback(demo-echodone);
		goto s|instructions;
	};
	# => {
hangup:
		Playback(demo-thanks);
		Hangup();
	};
	t => goto #|hangup;
	i => Playback(invalid);
};


Syntax Note
------------------------
Please note that all opening {'s are on the same line as the keyword.  For
the time being, that syntax is mandatory.  We are looking at ways to allow
other syntax in the future for flexibility, but for now, that is the way
you must write AEL clauses.