I think the commenter meant sending a specific function definition to the REPL, like in Common Lisp, Clojure, or F#'s REPLs, without re-evaluating the entire file, like how DrRacket does it. I think Racket has some functionality that allows it though, and I think the Racket Emacs mode supports it. I am not aware of how to do it with DrRacket.