bug#70392: 29.3; null info page is unclear

bug#70392: 29.3; null info page is unclear

[Tom DL]

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In GNU Emacs 29.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.41,
cairo version 1.18.0)
Windowing system distributor 'The X.Org Foundation', version 11.0.12101010
System Description: EndeavourOS

Configured using:
 'configure --with-x-toolkit=gtk3 --with-native-compilation=aot
 --sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
 --with-tree-sitter --localstatedir=/var --with-cairo
 --disable-build-details --with-harfbuzz --with-libsystemd
 --with-modules 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt
 -fexceptions -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security
 -fstack-clash-protection -fcf-protection -g
 -ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto'
 'LDFLAGS=-Wl,-O1 -Wl,--sort-common -Wl,--as-needed -Wl,-z,relro
 -Wl,-z,now -Wl,-z,pack-relative-relocs -flto=auto'
 'CXXFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt -fexceptions
 -Wp,-D_FORTIFY_SOURCE=2 -Wformat -Werror=format-security
 -fstack-clash-protection -fcf-protection -Wp,-D_GLIBCXX_ASSERTIONS -g
 -ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

Important settings:
  value of $LC_MONETARY: es_ES.UTF-8
  value of $LC_NUMERIC: es_ES.UTF-8
  value of $LC_TIME: es_ES.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-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
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg rfc6068
epg-config gnus-util text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
comp comp-cstr warnings icons subr-x rx cl-seq cl-macs gv cl-extra
help-mode bytecomp byte-compile cl-lib sendmail rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils rmc iso-transl tooltip cconv
eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode 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 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 nadvice seq simple cl-generic
indonesian philippine 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 emoji-zwj charscript charprop case-table epa-hook
jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 77244 5722)
 (symbols 48 7141 0)
 (strings 32 19706 2242)
 (string-bytes 1 597786)
 (vectors 16 15776)
 (vector-slots 8 329999 11158)
 (floats 8 27 46)
 (intervals 56 262 0)
 (buffers 984 11))



The info page "Predicates on Lists" has a section on `null` which is
confusing. It says:

…as a matter of clarity we use null when object is considered a list and
not when it is considered a truth value…

But my understanding is that we also use null when object is considered
a non-boolean value. E.g. if `foo` could be `red` `green` or `nil` then
`foo` is neither a list nor a truth value. The info page made me think I
should use `not` rather than `null`, but upon further research, it looks
like `null` is fine for checking for `nil` when `nil` isn't used to
represent falsity.

I would suggested rewording the info page to read as so:

…as a matter of clarity we use null when object is considered a list or
other non-boolean value. We use not when object is considered a boolean
value…

It may also be helpful to change the section on `not` in "Constructs for
Combining Conditions":

…we recommend using the name null if you are testing for an empty list
or other non-boolean nil.

Thanks for your consideration.

Tom Dalziel

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bug#70392: 29.3; null info page is unclear

[Eli Zaretskii]

> From: Tom DL <tom_dl@hotmail.com>
> Date: Mon, 15 Apr 2024 07:28:59 +0000
> 
> …as a matter of clarity we use null when object is considered a list and
> not when it is considered a truth value…
> 
> But my understanding is that we also use null when object is considered
> a non-boolean value. E.g. if `foo` could be `red` `green` or `nil` then
> `foo` is neither a list nor a truth value. The info page made me think I
> should use `not` rather than `null`, but upon further research, it looks
> like `null` is fine for checking for `nil` when `nil` isn't used to
> represent falsity.

'null' is fine here, but the manual describes this in a section about
lists, so that's why it contrasts between lists and booleans.

> I would suggested rewording the info page to read as so:
> 
> …as a matter of clarity we use null when object is considered a list or
> other non-boolean value. We use not when object is considered a boolean
> value…
> 
> It may also be helpful to change the section on `not` in "Constructs for
> Combining Conditions":
> 
> …we recommend using the name null if you are testing for an empty list
> or other non-boolean nil.

Thanks, I clarified the wording in these two cases, and I'm therefore
closing this bug.