bug#59666: closed (29.0.50; Eshell: comparisons such as {> 3 2} do not work in Eshell context)

[GNU bug Tracking System]

Your message dated Thu, 1 Dec 2022 20:38:43 -0500
with message-id 
<CAEc2VK2q35NbkcB7KxuAhZxAd_Qn4Ainw54Myftr_w7ebFm6Ow@mail.gmail.com>
and subject line Re: bug#59666: 29.0.50; Eshell: comparisons such as {> 3 2} do 
not work in Eshell context
has caused the debbugs.gnu.org bug report #59666,
regarding 29.0.50; Eshell: comparisons such as {> 3 2} do not work in Eshell 
context
to be marked as done.

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59666: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=59666
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--- Begin Message --- Subject: 29.0.50; Eshell: comparisons such as {> 3 2} do not work in Eshell context Date: Mon, 28 Nov 2022 19:15:41 -0500

Note: I am running this with the following hook removed:

(add-hook 'eshell-mode-hook
          (lambda ()
            (remove-hook
             'eshell-alternate-command-hook
             'eshell-fix-bad-commands t)))
However, not removing it makes no difference to the behavior, the error
visibility would be postponed until the 4th try, when eshell asks to 

provide an alias (making everything even more confusing).

===========
Bug report:
===========

All behavior of comparisons below is incorrect

# Comparisons using ">"
### 1.
~/tmp $ ${> 3 2}
Actual: nil: command not found: command not found
Expected: t: command not found (same as below in pure elisp)

~/tmp $ $(> 3 2) # pure elisp
Actual equals Expected: t: command not found


### 2.
~/tmp $ {> 3 2}
Actual: nil: command not found
Expected: t

### 3.
~/tmp $ > 3 2
nil: command not found
Expected: t
 
# the above shows incorrect result, which can be tested also as follows

### 4.
~/tmp $ if {> 3 2} {echo YES} {echo NO}
Actual: NO
Expected: YES

# Reverse comparisons using "<"

### 5.
~/tmp $ ${< 3 2}
Actual: Eshell does not support input redirection
Expected: nil: command not found

### 6.
~/tmp $ {< 3 2}
Actual: Eshell does not support input redirection
Expected: no result, as in (< 3 2)

### 7.
~/tmp $ < 3 2
Actual: Eshell does not support input redirection
Expected: nil: command not found
Expected: no result, as in (< 3 2)

### 8. The above shows incorrect results, which can be tested in
#      variants of the following:
~/tmp $ if {< 3 2} {echo YES} {echo NO}
Actual: Eshell does not support input redirection
Expected: NO



In GNU Emacs 29.0.50 (build 1, x86_64-suse-linux-gnu, GTK+ Version
3.24.34, cairo version 1.17.6)
System Description: openSUSE Tumbleweed

Configured using:
 'configure --host=x86_64-suse-linux-gnu --build=x86_64-suse-linux-gnu
 --program-prefix= --disable-dependency-tracking --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=/var/lib --mandir=/usr/share/man
 --infodir=/usr/share/info --disable-build-details --without-pop
 --with-mailutils --without-hesiod --with-gameuser=:games
 --with-kerberos --with-kerberos5 --with-file-notification=inotify
 --with-modules --enable-autodepend --prefix=/usr
 --mandir=/usr/share/man --infodir=/usr/share/info --datadir=/usr/share
 --localstatedir=/var --sharedstatedir=/var/lib
 --libexecdir=/usr/libexec --with-file-notification=yes
 --enable-locallisppath=/usr/share/emacs/29.0.50/site-lisp:/usr/share/emacs/site-lisp
 --without-x --with-json --without-xim --with-sound --with-xpm
 --with-jpeg --with-tiff --with-gif --with-png --with-rsvg --with-dbus
 --without-xft --without-gpm --with-pgtk --without-native-compilation
 --with-toolkit-scroll-bars --with-libotf --with-m17n-flt --with-cairo
 --without-xwidgets --with-dumping=pdumper 'CFLAGS=-O2 -Wall
 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=3 -fstack-protector-strong
 -funwind-tables -fasynchronous-unwind-tables -fstack-clash-protection
 -Werror=return-type -flto=auto -D_GNU_SOURCE
 -DGDK_DISABLE_DEPRECATION_WARNINGS -DGLIB_DISABLE_DEPRECATION_WARNINGS'
 LDFLAGS=-flto=auto'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY
PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS WEBP XIM GTK3 ZLIB

Important settings:
  value of $LANG: en_CA.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Eshell

Minor modes in effect:
  shell-dirtrack-mode: t
  eshell-prompt-mode: t
  eshell-hist-mode: t
  eshell-pred-mode: t
  eshell-cmpl-mode: t
  eshell-proc-mode: t
  eshell-arg-mode: t
  tooltip-mode: t
  global-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 sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils cl-seq rx
em-unix em-term term disp-table shell subr-x ehelp em-script em-prompt
em-ls em-hist em-pred em-glob em-extpipe em-cmpl em-dirs esh-var
pcomplete comint ansi-osc ansi-color ring em-basic em-banner em-alias
esh-mode eshell esh-cmd generator esh-ext esh-opt esh-proc esh-io
esh-arg esh-module esh-groups esh-util cus-edit pp cus-start cus-load
icons wid-edit cl-loaddefs cl-lib files-x rmc iso-transl tooltip cconv
eldoc paren electric uniquify ediff-hook vc-hooks lisp-float-type
elisp-mode mwheel term/pgtk-win pgtk-win term/common-win pgtk-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 dynamic-setting system-font-setting font-render-setting cairo
gtk pgtk lcms2 multi-tty make-network-process emacs)

Memory information:
((conses 16 78484 13781)
 (symbols 48 8942 0)
 (strings 32 24745 2566)
 (string-bytes 1 734947)
 (vectors 16 15111)
 (vector-slots 8 205050 17892)
 (floats 8 35 34)
 (intervals 56 421 0)
 (buffers 984 11))

--- End Message ---

--- Begin Message --- Subject: Re: bug#59666: 29.0.50; Eshell: comparisons such as {> 3 2} do not work in Eshell context Date: Thu, 1 Dec 2022 20:38:43 -0500

Thanks for your detailed follow up.

I understand what is happening, and am closing this issue (please reopen if you see fit).

In the closing notes, I have a suggestion (slash question), and a summary of how to use CONDITIONAL in the 'if' statement - in case it can be of use for someone reading later.

****** Suggestion / question

Would it be reasonable to suggest removing existing functionality as follows:

In the statement

if     CONDITIONAL { TRUE-COMMANDS } { FALSE-COMMANDS }

The CONDITIONAL can only have the following forms:

1. ${command-call}
2. ${function-call}

The currently allowed

3. {command-call}
4. (function-call)

would represent syntax error.

(3. is outright wrong as it brings silent invalid results)

By banning 3. and 4., Would Eshell lose the ability to express any semantics that can be achieved using 1. and 2?


****** Math operations using < or < in ~if CONDITIONAL~

~Quote < and >  as \< or \> with backslash OTHERWISE YOU GET AN ERROR, OR SILENTLY INCORRECT BEHAVIOR~

inside () or $() quotes are not needed but do not hurt

Examples:

if ${\< 3 5} {echo YES} {echo NO}   # YES -- correct
if ${< 3 5} {echo YES} {echo NO}    # Eshell thinks it is redirection, so WRONG
if ${> 3 5} {echo YES} {echo NO}    # YES - WRONG!!! (silently)

if $(< 3 5) {echo YES} {echo NO} # YES -- correct
if $(> 3 5) {echo YES} {echo NO} # NO  -- correct
if (< 3 5) {echo YES} {echo NO} # YES -- correct
if (> 3 5) {echo YES} {echo NO} # NO -- correct

****** Flow control: TL;DR of ~if CONDITIONAL~
 
- Bad:  Do NOT use ~if {function-call}~ (abbreviated, ~if {}~)
- Good: Do use     ~if ${function-call}~  or  ~if $(function-call)~ or ~if (function-call)~

 
Examples"
- Bad  use:  ~if {= 3 0}  { echo YES } { echo NO }~  # YES -- WRONG!!! (silently!!)
- Good use:  ~if ${= 3 0} { echo YES } { echo NO }~  # NO -- correct

****** Flow control: Recipe of ~if CONDITIONAL~

In flow control ~if CONDITIONAL {TRUE-COMMANDS} {FALSE-COMMANDS}~: do NOT USE the ~{}~ BLOCK as CONDITIONAL; instead use ~the ${}~, ~$()~ or ~()~ blocks. The ~$~ versions are preferred.

The above recipy also applies to ~unless~, ~while~ ~until~. (this does not apply to ~for VAR in LIST~ which is described elsewhere)

Thanks,

Milan

--- End Message ---