(cond-expand
 (chicken-5 (import (chicken file posix)))
 (else      (use posix)))

(define port
  (let ((check #t))
    (make-output-port
     (lambda (s)
       (file-write 2 s) ;; <-- this works
       ;;((lambda () (file-write 2 s))) ;; <-- this doesn't, in csi
       )
     (lambda () #t))))

;; expecting to see "ab..." output here:
(##sys#with-print-length-limit
 2
 (lambda () (##sys#print "abcdefg" #f port)))