(define-syntax assert
  (syntax-rules ()
    ((_ check val err-msg)
     (unless (check val)
       (display "WARNING: " (current-error-port))
       (display err-msg (current-error-port))
       (display ", val: " (current-error-port))
       (write val (current-error-port))
       (newline (current-error-port))))))