Koa 2.0 compatible code

[suhas-babyoye]

Could you please check the following code:

/**
 * @param {object} options
 * @returns {Function}
 */
function koaStylus(options) {
    const middleware = stylus.middleware(options);

    function compile(req, res) {
        return callback => {
            middleware(req, res, callback);
        };
    }

    return async function stylusMiddleware(ctx, next) {
        compile(ctx.req, ctx.res);
        return await next();
    };
}

This works.. I think. But could someone please explain how it works? What does calling compile do? It just returns a function right? How does that end up executing stylus middleware?