Issue: DESCRIBE-INTERACTIVE (Version 1)

[Kent M Pitman <KMP@STONY-BROOK.SCRC.Symbolics.COM>]

Issue:        DESCRIBE-INTERACTIVE
References:   DESCRIBE (p441)
Category:     CLARIFICATION
Edit history: 12-Sep-88, Version 1 by Pitman
Status:	      For Internal Discussion

Problem Description:

  DESCRIBE is not prohibited from behaving interactively. In some
  implementations it is, and in other implementations it is not.
  Users of systems in which DESCRIBE is not interactive may presume
  that it is safe to call DESCRIBE in a batch applications without
  hanging the application, which can lead to problems.

Proposal (DESCRIBE-INTERACTIVE:EXPLICITLY-VAGUE):

  Clarify that DESCRIBE is permitted (though not required) to
  require user input, and that such input should be negotiated
  through *QUERY-IO*.

  [Descriptive information would continue to go to *STANDARD-OUTPUT*.]

Test Case:

  The following kind of interaction would be permissible in
  implementations which chose to do it:

   (DEFVAR *MY-TABLE* (MAKE-HASH-TABLE))
   (SETF (GETHASH 'FOO *MY-TABLE*) 1)
   (SETF (GETHASH 'BAR *MY-TABLE*) 2)
   (SETF (GETHASH 'FOOBAR *MY-TABLE*) 3)
   (DESCRIBE *MY-TABLE*)
   #<EQ-HASH-TABLE 259> has 3 entries.
   Do you want to see its contents? (Yes or No) Yes

Rationale:

  This implements the status quo.

Current Practice:

  Symbolics Genera asks some questions interactively when describing
  some kinds of structured data structures, such as hash tables.
  Since users can define their own DESCRIBE methods and took their cue
  from the system, describing some user structures also require such
  interactions.

Cost to Implementors:

  None.

Cost to Users:

  User code which depended on DESCRIBE running without user interaction
  would have to be modified. Such code is not currently fully portable,
  however.

Cost of Non-Adoption:

  Users would not know the straight story about whether they should
  expect interaction from DESCRIBE.

Benefits:

  Implementations which don't do interactive querying in DESCRIBE only
  because their not 100% sure it's kosher would be free to do it.

Aesthetics:

  Some people might think it's not aesthetic for DESCRIBE to require user
  intervention. Not saying whether it's permissible is probably less
  aesthetic, though.

Discussion:

  Pitman thinks it's important to clarify this issue, but he isn't fussy
  about the particulars.

  This proposal is the minimal proposal for compatibility with current
  behavior. If anyone is adamant about wanting DESCRIBE not to require
  user intervention, they might want to circulate a competing proposal
  requesting an incompatible change prohibiting current behavior in some
  implementations.