defsetf不能定义last与nthcdr

[liushizhi]

在windows系统中：
在clozure common lisp中：?(defsetf nthcdr (index lst)(ele)......)返回NTHCDR
在clisp中：(defsetf nthcdr (index lst)(ele)......)返回NTHCDR
在steel bank common lisp中：(defsetf nthcdr (index lst)(ele)...)--error

; in: DEFSETF NTHCDR
; (LAMBDA (INDEX LST) (BLOCK NTHCDR 1))
; ==>
; #'(LAMBDA (INDEX LST) (BLOCK NTHCDR 1))
;
; caught STYLE-WARNING:
; The variable INDEX is defined but never used.
;
; caught STYLE-WARNING:
; The variable LST is defined but never used.

; (SB-INT:NAMED-LAMBDA (SB-IMPL::%DEFSETF NTHCDR)
; (#:SUBFORMS #:ENV ELE)
; (DECLARE (SB-C::LAMBDA-LIST (INDEX LST)))
; (DECLARE (IGNORE #:ENV))
; (APPLY (LAMBDA (INDEX LST) (BLOCK NTHCDR 1)) #:SUBFORMS))
;
; caught STYLE-WARNING:
; The variable ELE is defined but never used.
;
; compilation unit finished
; caught 3 STYLE-WARNING conditions

debugger invoked on a SYMBOL-PACKAGE-LOCKED-ERROR in thread
#<THREAD "main thread" RUNNING {23D30061}>:
  Lock on package COMMON-LISP violated when defining a setf-expander for NTHCDR
  while in package COMMON-LISP-USER.
See also:
  The SBCL Manual, Node "Package Locks"
  The ANSI Standard, Section 11.1.2.1.2

Type HELP for debugger help, or (SB-EXT:EXIT) to exit from SBCL.

restarts (invokable by number or by possibly-abbreviated name):
  0: [CONTINUE ] Ignore the package lock.
  1: [IGNORE-ALL ] Ignore all package locks in the context of this operation.

  2: [UNLOCK-PACKAGE] Unlock the package.
  3: [ABORT ] Exit debugger, returning to top level.

(PACKAGE-LOCK-VIOLATION #<PACKAGE "COMMON-LISP"> :SYMBOL NTHCDR :FORMAT-CONTROL
"defining a setf-expander for ~A" :FORMAT-ARGUMENTS (NTHCDR))

[Christophe Rhodes (csr21-cantab)]

 status invalid
 done

Hi,

liushizhi <email address hidden> writes:

> See also:
> The SBCL Manual, Node "Package Locks"
> The ANSI Standard, Section 11.1.2.1.2

The reason that this is an error in SBCL is documented in these sections
of the manual and the CL standard.

Christophe

[Paul F. Dietz (paul-f-dietz)]

A user can write conforming CL for this by shadowing NTHCDR with their own symbol. The definitions for this can of course invoke CL:NTHCDR as needed.