Issue:              SETF-FUNCTIONS-AGAIN
References:         SETF, FBOUNDP, FDEFINITION, DEFSTRUCT
Related issues:     Issue FUNCTION-NAME
                    Issue SETF-OF-APPLY
Category:           CLARIFICATION
Edit history:       V1, 13 May 90, Sandra Loosemore

Problem description:

The addition of SETF functions to the language has left some
lingering questions:

- Whether (FBOUNDP '(SETF <name>)) is supposed to be true of <name>s 
that have SETF methods (as defined with DEFSETF or DEFINE-SETF-METHOD)
defined, or only <name>s where there are globally defined
functions named (SETF <name>).  (Issue #17 from Loosemore's
list.)

- Whether DEFSTRUCT is required to generate SETF functions, or required
to generate SETF methods, or whether this is unspecified.  (Issue
#19)

- Whether SETF places defined in the standard are required to be
implemented by SETF functions, by SETF methods, or whether this
is unspecified.  (Issue #20)

- Whether it is permissible for a <name> to have both a SETF
method defined via DEFSETF or DEFINE-SETF-METHOD, and an associated
SETF function at the same time.  


Proposal (SETF-FUNCTIONS-AGAIN:MINIMAL-CHANGES):

  (1) Clarify that (FBOUNDP '(SETF <name>)) must return true if and
  only if there is a function named (SETF <name>) defined.  It must
  return NIL if <name> has a SETF method defined but not a SETF
  function.

  (2) Clarify that it is unspecified whether DEFSTRUCT generates
  SETF methods or SETF functions for non-:READ-ONLY slot accessors.

  (3) Clarify that, unless a SETF function is explicitly documented
  in the standard, it is unspecified whether SETF places defined in
  the standard must be implemented as SETF methods or SETF functions.
  In combination with item (1), this implies that it is unspecified
  whether (SETF <name>) is FBOUNDP for these standard SETF
  places.

  (4) Clarify that it is possible, but generally not very useful, 
  to have both a SETF method and a SETF function defined for the same
  name.

Rationale:

  This proposal requires minimal changes for implementors.

Current Practice:

  Most implementations use SETF methods (and not SETF functions)
  to implement DEFSTRUCT accessors and the standard SETF places.
  In most implementations, the namespaces for SETF methods and
  SETF functions are disjoint.

Cost to Implementors:

  Probably none.

Cost to Users:

  Probably none.

Cost of non-adoption:

  Imprecision in the language specification.

Performance impact:

  Probably not significant.

Benefits:

   The language specification is made more precise.

Esthetics:

  It would probably be better to specify whether standard SETF
  places must be implemented as SETF functions or as SETF
  methods, instead of leaving it explicitly vague.  See also
  issue SETF-OF-APPLY for one particular case (AREF) where it
  seems like a good idea to specify that the SETF place must be
  implemented as a SETF function.

Discussion:
