function foo(str, context) {
    return str.replace(/\{(\w+(?:\.\w+)*)\}/g, function(match, name) {
        var keys = name.split('.'), k, v = context;
        while ( k = keys.shift() ) {
            if (v[k] == undefined) {
                v = '';
                break;
            }
            v = v[k];
        }
        return v;
    });
}

function parse(str) {
    var re = /\{\{(.?)\}\}|\{%(.*?)%\}/g;


}

template = '<ul class="comments">{% for comment in comments %}<li><a href="{{comment.author_link}}">{{comment.author_name}}</a>, <time>{{comment.datetime}}</time><p>{{comment.text}}</p></li>{% /for %}</ul>';