#lang cli
is not a part of Racket, so that’s why you need to additionally install it. Yes, it appears to be a DSL for writing a command-line program.
Racket already has a standard library for command-line parsing. Take a look at https://docs.racket-lang.org/reference/Command-Line_Parsing.html. Without using #lang cli
, your program size may be reduced by a bit.