Macros can be used during the compilation process in order to generate custom code, but they can also be used to perform some pre-compilation tasks.

These compiler configuration macros can be used with the haxe --macro commandline parameter.

An example is to force the inclusion of all the files defined in a given package and its sub packages :

haxe --macro include('my.package') ....

Please use single-quotes for string constants since some OS (such as Windows) remove double-quotes.

The previous example is actually a shortcut for the following :

haxe --macro haxe.macro.Compiler.include('my.package') ....

And here's the code for the actual method :

public static function include( pack : String, ?rec = true ) {
    for( p in Context.getClassPath() ) {
        var p = p + pack.split(".").join("/");
        if( !neko.FileSystem.exists(p) || !neko.FileSystem.isDirectory(p) )
            continue;
        for( file in neko.FileSystem.readDirectory(p) ) {
            if( StringTools.endsWith(file, ".hx") ) {
                var cl = pack + "." + file.substr(0, file.length - 3);
                Context.getModule(cl);
            } else if( rec && neko.FileSystem.isDirectory(p + "/" + file) )
                include(pack + "." + file, true, ignore);
        }
    }
}

As you can see, there's no black magic going here. You can use any of the haxe.macro.Compiler methods or write your own custom versions.

So far the possibilities include :

• including files to make sure they are compiled
• excluding some classes from being generated
• patching types by removing some declared fields or changing their type
• adding metadata either before/class is defined or at end of compilation (with Context onGenerate method)
• defining a custom Javascript code generator (see below)

Much more possibilities will be added when there is a need for it.

Custom JS Generator

You can write your own custom JS generator in haXe : the generator will take care of creating the .js file(s) and generating the class structure/registration. You cannot however customize the way the haXe expressions are generated.

See haxe/std/haxe/macro/DefaultJSGenerator.hx as a reference implementation.

In order to use it, simply add the following commandline parameter to haxe compilation :

--macro haxe.macro.DefaultJSGenerator.use()