I made a copy-paste mistake, the replacement for the last line of "MyLang.rkt" should use "body2" instead of "body":
#'(#%plain-module-begin (module nm lng (#%plain-module-begin . body2))) -- You received this message because you are subscribed to the Google Groups "Racket Users" group. To unsubscribe from this group and stop receiving emails from it, send an email to racket-users+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.