loader.vala

using GI;

public void main(string[] args)
{
    try {
        string name = "mymodule";
        Repository repository = Repository.get_default();

        unowned Typelib module = repository.require_private(
                Path.get_dirname(args[0]),
                name, null, RepositoryLoadFlags.IREPOSITORY_LOAD_FLAG_LAZY);

        BaseInfo _module_entry_point = repository.find_by_name(name, "module_entry_point");

        if (_module_entry_point == null)
        {
            stderr.printf("No 'module_entry_point' function found in module '%s'\n", name);
            return;
        }

        if (_module_entry_point.get_type() != InfoType.FUNCTION)
        {
            stderr.printf("Member 'module_entry_point' is a %s instead of a function\n", InfoType.to_string(_module_entry_point.get_type()));
            return;
        }

        string symbol = FunctionInfo.get_symbol((FunctionInfo)_module_entry_point);
        void *func = null;

        if (!module.symbol(symbol, &func))
        {
            stderr.printf("Could not extract symbol '%s' from module %s\n", symbol, name);
            return;
        }

        Argument input = (Argument)null;
        Argument output = (Argument)null;
        Argument ret = Argument();
        stdout.printf("TRACE 1\n");
        CallableInfo.invoke((CallableInfo)_module_entry_point, func, input, 0, output, 0, ret, false, true);
        stdout.printf("TRACE 2\n");
    }
    catch (Error err)
    {
        stderr.printf("Caught error: %s\n", err.message);
    }
}

mymodule.vala

namespace MyModule
{
    public void module_entry_point()
    {
        stdout.printf("Called MyModule.module_entry_point()\n");
    }
}

wscript

top = '.'
out = 'build'

def options(opt):
    opt.load('compiler_c')
    opt.load('vala')

def configure(conf):
    conf.load('compiler_c')
    conf.load('vala')

    conf.find_program('g-ir-compiler', var='G_IR_COMPILER')
    conf.check_cfg(package='gobject-introspection-1.0', uselib_store='GOBJECT_INTROSPECTION', args='--cflags --libs')

def build(bld):
    _build_module(bld,
        packages = '',
        target   = 'mymodule',
        uselib   = 'GLIB',
        source   = 'mymodule.vala',
        gir      = 'mymodule-1.0',
        pkg_name = 'mymodule'
    )

    bld.program(
        packages = 'gobject-introspection-1.0',
        target   = 'loader',
        uselib   = 'GOBJECT_INTROSPECTION',
        source   = 'loader.vala'
    )

def _build_module(bld, **kw):
    bld.shlib(**kw)

    gir = kw.get('gir', None)
    if gir:
        bld(
            rule   = '${G_IR_COMPILER} -o ${TGT} ${SRC}',
            source = '%s.gir' % gir,
            target = '%s.typelib' % gir,
        )