This code:
#lang racket
(display (vector->string #(#\H #\i #\!)))
is giving me this error message
Welcome to DrRacket, version 8.14 [cs].
Language: Beginning Student; memory limit: 128 MB.
read-syntax: `#lang` not enabled
possible reason: not allowed again inside a module that already starts `#lang`, or not enabled for interactive evaluation
when I try to run it. (also "#lang" gets highlighted with red/pink background in the editor) I have this exact statement at the start of two other programs that do run so I don't know why there is an error for this one. If I take "#lang racket" out it tells me it doesn't know what "display" is so "not allowed again" doesn't appear to be true.
This error was caused by the setting of MenuBar->Language->ChooseLanguage. It was set to "Teaching Languages"->Beginning Student (The error also occurs if "Advanced Student" is selected). Setting it to "The Racket Language" causes the error to go away. The Teaching Languages setting probably sets it to a (subset of) regular Scheme .
The error also occurs on the command line (racket myprogram.rkt), depending on the Language setting that is in the IDE (the "Save" floppy disk icon has to be pressed in order to change the command line behavior from a new Language setting).