situation.  The printer resets the column to
          ;; 0 by printing a newline, but we then advance it by printing
          ;; the prompt.  However the port-column of the output port
          ;; does not typically correspond with the actual column on the
          ;; screen, because the input is echoed back!  Since the
          ;; input is line-buffered and thus ends with a newline, the
          ;; output will really start on column zero.  So, here we zero
          ;; it out.  See bug 9664.
          ;;
          ;; Note that for similar reasons, the output-line will not
          ;; reflect the actual line on the screen.  But given the
          ;; possibility of multiline input, the fix is not as
          ;; straightforward, so we don't bother.
          ;;
          ;; Also note that the readline implementation papers over
          ;; these concerns, because it's readline itself printing the
          ;; prompt, and not Guile.
          (set-port-column! (current-output-port) 0)))
    (force-output)
    (run-hook before-read-hook)
    ((or reader read) (current-input-port))))