RacketCon 2021 - Shrubbery Notation - Matthew Flatt 

Shrubbery notation is similar to S-expression notation, but instead of generating fully formed trees, it is intended to partially group input for further enforestation by another parser (e.g., as in Honu). The notation is line- and indentation-sensitive, and the parsed form of a shrubbery imposes grouping to ensure that further parsing is consistent with the shrubbery’s lines and indentation.
Bio: Matthew Flatt is a professor at the University of Utah and one of the main developers of Racket. He has worked primarily on Racket’s macro system, run-time system, and compiler.