function parseToAsync(expression, options) {
        var parsedExpression = parse(expression, options);
        return function (path, basename, siblingsFn) {
            var result = parsedExpression(path, basename, siblingsFn);
            return result instanceof winjs_base_1.TPromise ? result : winjs_base_1.TPromise.as(result);
        };
    }
Same as `parse`, but the ParsedExpression is guaranteed to return a Promise