Question about Presentations

[miller@GEM.cam.nist.gov (Bruce R. Miller)]

    Date: Sat, 13 Oct 90 19:35 EDT
    From: RWK@fuji.ila.com (Robert W. Kerns)

	Date: Fri, 12 Oct 90 14:50:08+0900
	From: kddlab!harl.hitachi.co.jp!mklein@uunet.uu.net
	I am trying to "present" an object to a screen with a label different
	from the usual printed representation of the object. When I mouse-select
	...
		Thanks very much,

			Mark Klein
			...
    Konban wa, Kurain-san.

    The problem is your use of (FORMAT STREAM "~A" LABEL), if label
    is not a string, creates a presentation, because FORMAT calls
    WRITE in that case.  This presentation will be a SYMBOL presentation,
    and since SYMBOL is a subtype of EXPRESSION, it will satisfy your
    call to ACCEPT.  (When multiple presentations could apply, the system
    always chooses the innermost).

    Here are a couple ways to do what you want:

    (defun present-as (object label &key (stream *standard-output*))
      "Presents object to stream with given label"
      (dw:with-output-as-presentation (:single-box t
				       :type (type-of object)
				       :stream stream
				       :object object)
	(format stream "~a" (string label))))

    Or more efficiently:

    (defun present-as (object label &key (stream *standard-output*))
      "Presents object to stream with given label"
      (dw:with-output-as-presentation ...
	(write-string (string label) stream)))

Alternatively, you could use 

    (defun present-as (object label &key (stream *standard-output*))
      "Presents object to stream with given label"
      (dw:with-output-as-presentation (:single-box t
				       :type (type-of object)
				       :stream stream
				       :ALLOW-SENSITIVE-INFERIORS NIL
				       :object object)
	(print-any-way-you-like label stream)))

This avoids second guessing the various print functions, especially if
the `label' evolves into a more complicated call to format.  It also
disables any nested presentations that you might WANT sensitive.

bruce