If you think that's the fun part (lots of people don't) you should look at a Nomic. https://en.wikipedia.org/wiki/Nomic

That just sounds like Calvinball.

It seems unlikely that Calvinball is a nomic. Instead Calvinball appears to be more like Mornington Crescent, in that players are all participating in creating a mutually satisfying fiction, Calvinball's fiction looks like a complicated ballgame, Mornington Crescent more cerebral but since in both cases there aren't actually any set rules the game is not about changing the rules. Rosalyn eventually figures out how to play Calvinball well just as players can get "good" at Mornington Crescent with experience.

That's just a terrific tip, you made my morning, thank you.

https://en.wikipedia.org/wiki/Mornington_Crescent_(game)

It's kinda neat for programmers too, since it's stack-based.