Even though it was at one point a physical book, I think, it's really a regularly updated documentation for the library. Sometimes it's not fully updated becaus

Even though it was at one point a physical book, I think, it's really a regularly updated documentation for the library. Sometimes it's not fully updated because it's written by one guy (Michael Snoyman, who also leads Yesod), but it always gets fully updated for the new version. It's not like a print book where you have to wait for the 2nd edition to come out.