(define (main)
  (define (print-it it)
    (display it))
  (define test "oooo")
  (print-it test))

(let ((output-port (open-file "test.txt" "w")))
  (display "hello, world" output-port)
  (newline output-port)
  ((main) output-port) ;; ERROR: Wrong type to apply: #<unspecified>
  (close output-port))