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Issue SETF-FUNCTIONS-AGAIN Writeup

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:


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