These are books, like digital literature, computer-generated poetry and MUDs, where a “nontrivial effort is required to allow the reader to traverse the text”. And they are more common than you might think, especially in geek culture. Game books that allow you to “choose your own adventure” are ergodic, as are fantasy novels with extensive maps and world-building notes. But the RPG handbook pushes ergodic reading to its limit.
I have a fair-sized collection of RPG books: the Advanced Fighting Fantasy books (Dungeoneer, Blacksand!, Allansia, Out of the Pit, and Titan), Savage Worlds, D&D 4E Players Handbook, Mythic, the full set of D&D 5E Manuals (plus some others I’ve forgotten about, no doubt), but I’m yet to really play one.
I once convinced a friend to start an AFF quest, we must have been about 11 or 12, but our story didn’t get much further than one night. More commonly I’d spend hours meticulously constructing characters (on the slim chance I could ever get someone to play) and reading and re-reading the quests and background lore to imprint the worlds and stories in my mind.
Since I bought 5E I’m pretty much back there 20 years on, rolling characters and questing in my imagination.