I have modified print/main.rkt. How do I test it? It doesn’t get built when I run make at the top-level. I can see my modification working when directly running against io/main.rkt though.

You need to run make in racket/src/cs. (The racket/src/io/README.txt points to racket/src/cs/README.txt to explain, but there’s a lot of information to wade through.)

Thanks! Now I see make inside racket/src/cs changes the schemified libaries. It’s working now.