Mastering Functional Programming

Asynchrony with IO

The central domain of the application of the Cats effect is asynchronous programming. Asynchronous programming is an event-driven style of programming, where you do not waste threads and other resources on blocking, waiting for some event to happen.

Consider, for example, that you have a web server that handles incoming HTTP requests. It has a pool of threads that are used by the server to handle each request. Now, the handlers themselves may require some blocking operations. For example, contacting a database for contacting an external HTTP API can be a potentially blocking operation. This is because the database or an HTTP API does not respond immediately as a rule. This means that if a request handler needs to contact ...