Issue MACROEXPAND-HOOK-INITIAL-VALUE Writeup

Forum:		Public Review

Issue:		MACROEXPAND-HOOK-INITIAL-VALUE

References:	Moon's public review comment #15

		*MACROEXPAND-HOOK* (p. 3-78)

Category:	CHANGE

Edit history:	21 Dec 1992, Version 1 by Loosemore

Status:         Proposal IMPLEMENTATION-DEPENDENT passed 9-0-0, Mar 1993



Problem description:


  Page 3-78 says the initial value of *macroexpand-hook* is "a

  designator for the function funcall". I think the initial value should

  be implementation dependent, because some implementations use

  *macroexpand-hook* to provide information to their program development

  environment on which macros are in use.



Proposal (MACROEXPAND-HOOK-INITIAL-VALUE:IMPLEMENTATION-DEPENDENT):


  (1) Change the description of the initial value of *MACROEXPAND-HOOK*

  to say that it is a designator for a function that is equivalent to

  the function FUNCALL, but which can have additional 

  implementation-dependent side-effects.


  (2) Add to the notes section of the dictionary entry for

  *MACROEXPAND-HOOK* a statement that users who put their own function

  into *MACROEXPAND-HOOK* should consider saving the previous hook and

  calling it from their function.



Rationale:


  Adopting this proposal would make *MACROEXPAND-HOOK* more useful.



Current practice:


  Unknown.



Cost to implementors:


  None.



Cost to users:


  Probably little or none.



Aesthetics:


  Neutral.



Editorial impact:


  The change is confined to the dictionary entry for *MACROEXPAND-HOOK*.



Discussion: