[Антон Крамолов]

Очевидный фикс:

exports.render = function(filename) {
    var source = fs.readFileSync(filename, 'utf-8');
    var compiled = compile(source);

    return function(obj) {
        return new Function('vars', 'vars=vars||{};var out="";with(vars){' + 
            compiled + '};return out')(obj);
    }
}