setq failure following list manipulation

setq failure following list manipulation

[Bill Lytton]

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In GNU Emacs 21.3.1 (x86_64-redhat-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2005-08-09 on dolly.build.redhat.com
configured using `configure  --host=x86_64-redhat-linux --build=x86_64-redhat-linux --target=x86_64-redhat-linux-gnu --program-prefix= --prefix=/usr --exec-prefix=/usr --bindir=/usr/bin --sbindir=/usr/sbin --sysconfdir=/etc --datadir=/usr/share --includedir=/usr/include --libdir=/usr/lib64 --libexecdir=/usr/libexec --localstatedir=/var --sharedstatedir=/usr/com --mandir=/usr/share/man --infodir=/usr/share/info --with-pop --with-sound'
Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8
  default-enable-multibyte-characters: t

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

bug or feature?:

quoted arg for setq in function call no longer works after maninpulating list
using global variable

(defun ae ()  (setq nums '(1 2 3)))
(nconc nums (list 4))
(ae) ;; returns (1 2 3 4)
nums ;; returns (1 2 3 4)

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Re: setq failure following list manipulation

[Kevin Rodgers]

Bill Lytton wrote:
 > bug or feature?:
 >
 > quoted arg for setq in function call no longer works after 
maninpulating list
 > using global variable
 >
 > (defun ae ()  (setq nums '(1 2 3)))
 > (nconc nums (list 4))
 > (ae) ;; returns (1 2 3 4)
 > nums ;; returns (1 2 3 4)

I think you meant to call (ae) before (nconc nums (list 4)), since
otherwise nums would not be bound.  So, after (ae) nums is bound to
this cons cell structure:

+-+-+  +-+-+  +-+-+
| | +->| | +->| |*|
+++-+  +++-+  +++-+
  |      |      |
  v      v      v
  1      2      3

and after (nconc nums (list 4)) the last cons cell is modified so that
the structure (to which nums is still bound) is this:

+-+-+  +-+-+  +-+-+  +-+-+
| | +->| | +->| | +->| |*|
+++-+  +++-+  +++-+  +++-+
  |      |      |      |
  v      v      v      v
  1      2      3      4

-- 
Kevin Rodgers
Sr. Software Engineer, IHS