I see that I 'forgot' to copy-paste the first sentence of my original
report, which was:

I am trying examples from Paul Graham's book 'On lisp', but using EIEIO.

On Thu, 7 Oct 2021 at 08:31, dalanicolai <dalanicolai@gmail.com> wrote:

> I have encountered the following confusing behavior (and 'regression'
> compared to Emacs 27).
>
> Starting from emacs -Q, in Emacs 27 when I try to evaluate the following
> code:
>
>
> (require 'eieio)
>
> (defclass rectangle ()
>   (height width))
>
>
> different than in CLOS, Emacs errors with:
> '(wrong-type-argument listp height)'
>
> When I evaluate the same code in Emacs 28 then Emacs does not return an
> error.
>
> However, if I subsequently try to initialize the slots using:
>
>
> (let ((r (make-instance rectangle)))
>   (setf (slot-value r 'height) 2
>         (slot-value r 'width) 3))
>
>
> then Emacs 28 does return an error. If I replace the code to create the
> class with (adding the parentheses around the slots):
>
>
> (defclass rectangle ()
>   ((height) (width)))
>
>
> then the code above for initializing the slots works as expected (and
> similar behavior when using oref). Which means that also in Emacs 28 the
> parentheses are required. So Emacs 27 correctly errors when not using them,
> but Emacs 28 suggests that things are alright when omitting the parentheses
> which is incorrect and confusing.
>
> Then additionally, the requirement of the parentheses is, as far as I
> could find, not explicitly mentioned as a 'difference from CLOS' in the
> manual, which 'additionlly' is confusing.
>
>
>
> In GNU Emacs 28.0.50 (build 3, x86_64-pc-linux-gnu, GTK+ Version 3.24.30,
> cairo version 1.17.4)
>  of 2021-09-06 built on daniel-fedora
> Repository revision: c4724add006e62b81f847937db56335a81bdcc74
> Repository branch: master
> Windowing system distributor 'The X.Org Foundation', version 11.0.12011000
> System Description: Fedora 34 (Workstation Edition)
>
> Configured using:
>  'configure --with-mailutils --with-cairo --with-modules --with-pgtk
>  --with-native-compilation'
>
> Configured features:
> ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
> JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
> NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG RSVG SECCOMP SOUND THREADS TIFF
> TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK3 ZLIB
>
> Important settings:
>   value of $LANG: en_US.UTF-8
>   value of $XMODIFIERS: @im=none
>   locale-coding-system: utf-8-unix
>
> Major mode: Lisp Interaction
>
> Minor modes in effect:
>   tooltip-mode: t
>   global-eldoc-mode: t
>   eldoc-mode: t
>   electric-indent-mode: t
>   mouse-wheel-mode: t
>   tool-bar-mode: t
>   menu-bar-mode: t
>   file-name-shadow-mode: t
>   global-font-lock-mode: t
>   font-lock-mode: t
>   blink-cursor-mode: t
>   auto-composition-mode: t
>   auto-encryption-mode: t
>   auto-compression-mode: t
>   line-number-mode: t
>   indent-tabs-mode: t
>   transient-mark-mode: t
>
> Load-path shadows:
> None found.
>
> Features:
> (shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
> rfc822 mml mml-sec epa derived epg rfc6068 epg-config gnus-util rmail
> rmail-loaddefs auth-source password-cache json map text-property-search
> seq mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev
> gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util
> mail-prsvr mail-utils help-fns radix-tree cl-print debug backtrace
> help-mode find-func cl-seq eieio byte-opt bytecomp byte-compile cconv
> eieio-core cl-macs gv eieio-loaddefs time-date subr-x cl-loaddefs cl-lib
> iso-transl tooltip eldoc electric uniquify ediff-hook vc-hooks
> lisp-float-type mwheel term/x-win x-win term/common-win x-dnd tool-bar
> dnd fontset image regexp-opt fringe tabulated-list replace newcomment
> text-mode elisp-mode lisp-mode prog-mode register page tab-bar menu-bar
> rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
> font-lock syntax font-core term/tty-colors frame minibuffer cl-generic
> cham georgian utf-8-lang misc-lang vietnamese tibetan thai tai-viet lao
> korean japanese eucjp-ms cp51932 hebrew greek romanian slovak czech
> european ethiopic indian cyrillic chinese composite charscript charprop
> case-table epa-hook jka-cmpr-hook help simple abbrev obarray
> cl-preloaded nadvice button loaddefs faces cus-face macroexp files
> window text-properties overlay sha1 md5 base64 format env code-pages
> mule custom widget hashtable-print-readable backquote threads dbusbind
> inotify lcms2 dynamic-setting system-font-setting font-render-setting
> cairo move-toolbar gtk x-toolkit x multi-tty make-network-process
> native-compile emacs)
>
> Memory information:
> ((conses 16 74940 7555)
>  (symbols 48 7056 0)
>  (strings 32 21134 1155)
>  (string-bytes 1 724821)
>  (vectors 16 13991)
>  (vector-slots 8 277232 15363)
>  (floats 8 26 33)
>  (intervals 56 281 0)
>  (buffers 992 13))
>
>
>