Issue EVAL-WHEN-OBSOLETE-KEYWORDS Writeup

Forum:		Public Review

Issue:		EVAL-WHEN-OBSOLETE-KEYWORDS

References:	Moon's public review comment #2 (X3J13/92-3202)

		EVAL-WHEN

		Issue EVAL-WHEN-NON-TOP-LEVEL

Category:	CHANGE

Edit history:	20 Dec 1992, Version 1 by Loosemore

		08 Jan 1993, Version 2 by Loosemore (comments from Moon)

		12 Sept 1993, Version 3 by Loosemore (add second proposal)

Status:         Proposal REMOVE-OLD-KEYWORDS failed 3-6-0, March 1993

		Proposal X3J13-MARCH-1993 passed 6-1, March 1993



Problem description:


  The language in draft 12.24 about the relationship between

  the new EVAL-WHEN keywords :EXECUTE, :COMPILE-TOPLEVEL, and

  :LOAD-TOPLEVEL and the old, deprecated keywords EVAL, COMPILE, and 

  LOAD is confusing.  (For example, it's inconsistent about what

  EVAL means when not at top level.)  The compatibility argument

  for retaining two sets of keywords with slightly different

  meanings is outweighed by the resulting confusion.



Proposal (EVAL-WHEN-OBSOLETE-KEYWORDS:REMOVE-OLD-KEYWORDS):


  Eliminate all mention of the old keywords EVAL, COMPILE, and LOAD

  in connection with EVAL-WHEN.


Proposal (EVAL-WHEN-OBSOLETE-KEYWORDS:X3J13-MARCH-1993):


  Generalize the use of the old keywords; define that eval-when always 

  treats eval the same as :execute, compile the same as :compile-toplevel,

  and load the same as :load-toplevel.



Rationale:


  Adopting this suggestion would shorten the specification and remove

  an inconsistency.  There are so many incompatibilities between

  CLtL1, CLtL2, and the draft standard that it's pointless to try to

  allow for a modeless implementation that is simultaneously compatible

  with all of them.



Current practice:


  Moon says he's not aware of any implementations whose current releases

  don't support the new keywords.



Cost to implementors:


  Probably small; implementations could continue to support the old

  keywords as an extension.



Cost to users:


  This is an incompatible change, but one that is easy to detect.  A

  good implementation should complain about unrecognized EVAL-WHEN

  keywords, anyway.



Aesthetics:


  Making the standard simpler is a good thing.



Editorial impact:


  The dictionary entry for EVAL-WHEN is the only place affected.

  (The discussion of EVAL-WHEN in the concept section relating to

  file compilation uses the new keywords exclusively.)



Discussion:


  Moon says: 

    I like EVAL-WHEN-NON-TOP-LEVEL:REMOVE-OLD-KEYWORDS (version 1).


  Moon suggested (in his public review comment) that another way to 

  resolve this problem would be to define the behavior of the old 

  keywords to be exactly the same as that of the new keywords.