Moved GUI import to main submodule

tm/expander.rkt

 #lang br/quicklang
 
 (require (except-in tm/tmachine run)
-         (only-in tm/gui simulate)
          racket/set)
 
 (provide (rename-out [tm-module-begin #%module-begin])
@@ -114,6 +113,7 @@
      (define this-tm
        (make-tm-config raw-prgm))
      (module+ main
+       (require (only-in tm/gui simulate))
        (display "Input string: ")
        (define input (read-line))
        (set-input! this-tm input)