Appending to a list

Appending to a list

[steve-humphreys]

Would appending to list like this be good?

(setq bird '("Toucan" "King Fisher"))
(setq bird (append bird ("Swift") ))

Or does one customarily use other constructs for
adding to a list?

Re: Appending to a list

[Joost Kremers]

On Sun, Dec 13 2020, steve-humphreys@gmx.com wrote:
> Would appending to list like this be good?
>
> (setq bird '("Toucan" "King Fisher"))
> (setq bird (append bird ("Swift") ))

This should result in an error, because `("Swift")` isn't quoted. You'd need:

    (setq bird (append bird '("Swift")))

But note that the last argument of `append` isn't copied, so it may not be a
good idea to use a literal list.

> Or does one customarily use other constructs for
> adding to a list?

`push` is what I would use:

    (push "Swift" bird)

No need to use `setq` here.

`push` won't check if the element is already in the list, though. You can use
`cl-pushnew` in that case, but be sure to load the library it's in:

    (require 'cl-lib)
    (cl-pushnew "Swift" bird)

HTH

-- 
Joost Kremers
Life has its moments

Re: Appending to a list

[Óscar Fuentes]

Joost Kremers <joostkremers@fastmail.fm> writes:

> On Sun, Dec 13 2020, steve-humphreys@gmx.com wrote:
>> Would appending to list like this be good?
>>
>> (setq bird '("Toucan" "King Fisher"))
>> (setq bird (append bird ("Swift") ))
>
> This should result in an error, because `("Swift")` isn't quoted. You'd need:
>
>     (setq bird (append bird '("Swift")))
>
> But note that the last argument of `append` isn't copied, so it may not be a
> good idea to use a literal list.
>
>> Or does one customarily use other constructs for
>> adding to a list?
>
> `push` is what I would use:
>
>     (push "Swift" bird)

This does not append.

> No need to use `setq` here.
>
> `push` won't check if the element is already in the list, though. You can use
> `cl-pushnew` in that case, but be sure to load the library it's in:
>
>     (require 'cl-lib)
>     (cl-pushnew "Swift" bird)

Isn't that the same as

(add-to-list bird "Swift" t)

?

Re: Appending to a list

[steve-humphreys]

> Sent: Sunday, December 13, 2020 at 10:03 PM
> From: "Joost Kremers" <joostkremers@fastmail.fm>
> To: steve-humphreys@gmx.com
> Cc: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
>
> On Sun, Dec 13 2020, steve-humphreys@gmx.com wrote:
> > Would appending to list like this be good?
> >
> > (setq bird '("Toucan" "King Fisher"))
> > (setq bird (append bird ("Swift") ))
>
> This should result in an error, because `("Swift")` isn't quoted. You'd need:
>
>     (setq bird (append bird '("Swift")))
>
> But note that the last argument of `append` isn't copied, so it may not be a
> good idea to use a literal list.
>
> > Or does one customarily use other constructs for
> > adding to a list?
>
> `push` is what I would use:
>
>     (push "Swift" bird)
>
> No need to use `setq` here.
>
> `push` won't check if the element is already in the list, though. You can use
> `cl-pushnew` in that case, but be sure to load the library it's in:
>
>     (require 'cl-lib)
>     (cl-pushnew "Swift" bird)

It won't be already in the list.  Basically I just want to push entries
that are themselves lists, and just go with push push push ...

That was very helpful Joost.

> HTH
>
> --
> Joost Kremers
> Life has its moments
>
>

Re: Appending to a list

[steve-humphreys]

> Sent: Sunday, December 13, 2020 at 10:30 PM
> From: "Óscar Fuentes" <ofv@wanadoo.es>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> Joost Kremers <joostkremers@fastmail.fm> writes:
> 
> > On Sun, Dec 13 2020, steve-humphreys@gmx.com wrote:
> >> Would appending to list like this be good?
> >>
> >> (setq bird '("Toucan" "King Fisher"))
> >> (setq bird (append bird ("Swift") ))

Can one just append lists together, then store the result to one of the variables, as I did?  
Or could such an approach lead to unintended consequences in some circumstances?

Regards
Steve

> > This should result in an error, because `("Swift")` isn't quoted. You'd need:
> >
> >     (setq bird (append bird '("Swift")))
> >
> > But note that the last argument of `append` isn't copied, so it may not be a
> > good idea to use a literal list.
> >
> >> Or does one customarily use other constructs for
> >> adding to a list?
> >
> > `push` is what I would use:
> >
> >     (push "Swift" bird)
> 
> This does not append.
> 
> > No need to use `setq` here.
> >
> > `push` won't check if the element is already in the list, though. You can use
> > `cl-pushnew` in that case, but be sure to load the library it's in:
> >
> >     (require 'cl-lib)
> >     (cl-pushnew "Swift" bird)
> 
> Isn't that the same as
> 
> (add-to-list bird "Swift" t)
> 
> ?
> 
> 
>

Re: Appending to a list

[Joost Kremers]

On Sun, Dec 13 2020, Óscar Fuentes wrote:
> Joost Kremers <joostkremers@fastmail.fm> writes:
>> On Sun, Dec 13 2020, steve-humphreys@gmx.com wrote:
>>> Or does one customarily use other constructs for
>>> adding to a list?
>>
>> `push` is what I would use:
>>
>>     (push "Swift" bird)
>
> This does not append.

Not in the Elisp sense, no. But in e.g., Python, `append` is the function that's
used to add an element to a list and the OP indicated that that's what he was
after.

>>     (require 'cl-lib)
>>     (cl-pushnew "Swift" bird)
>
> Isn't that the same as
>
> (add-to-list bird "Swift" t)

The doc string of `add-to-list` says that it should really only be used on
configuration variables in one's init file. For some reason (that I admittedly do
not understand), `add-to-list` shouldn't be used on lexical variables.

-- 
Joost Kremers
Life has its moments

Re: Appending to a list

[Stefan Monnier]

>> `push` is what I would use:
>>     (push "Swift" bird)
>
> This does not append.

Indeed, and it's a feature: append costs O(n), both in immediate CPU
time and in memory allocations (which can increase memory use or at
least increase the time spent in the GC) where `n` is the length of the
list to which you append.  So if you do that O(n) times, you get an
overall O(n²) complexity.

IOW, in most cases you're really better off with pushing to the
beginning of the list, and if the order doesn't suit you, then use
`reverse` afterwards, which will still be O(n) overall rather than
O(n²).

>> No need to use `setq` here.
>>
>> `push` won't check if the element is already in the list, though. You can use
>> `cl-pushnew` in that case, but be sure to load the library it's in:
>>
>>     (require 'cl-lib)
>>     (cl-pushnew "Swift" bird)
> Isn't that the same as
> (add-to-list bird "Swift" t)

Not quite:

- your `t` at the end makes `add-to-list` add to the rear of the
  list whereas `cl-pushnew` adds it to the front.
- `add-to-list` would require you to quote the variable symbol, as in:

      (add-to-list 'bird "Swift" t)

- `add-to-list` cannot operate on a lexically scoped `bird` variable.

- `add-to-list` cannot operate on generalized variables, whereas
  `cl-pushnew` (just like `push`) will be happy with things like

      (cl-pushnew "Swift" (gethash "birds" table))

- `cl-pushnew` by default compares with `eql` whereas here you'd likely
  want to compare with `equal`, like `add-to-list` does, so you'd need:

      (cl-pushnew "Swift" bird :test #'equal)

BTW `push` is significantly faster than either of `add-to-list` or
`cl-pushnew` since it doesn't need to check in O(n) time if the
element is already on the list.


        Stefan

Re: Appending to a list

[Joost Kremers]

On Sun, Dec 13 2020, Joost Kremers wrote:
> On Sun, Dec 13 2020, Óscar Fuentes wrote:
>> Joost Kremers <joostkremers@fastmail.fm> writes:
>>> On Sun, Dec 13 2020, steve-humphreys@gmx.com wrote:
>>>> Or does one customarily use other constructs for
>>>> adding to a list?
>>>
>>> `push` is what I would use:
>>>
>>>     (push "Swift" bird)
>>
>> This does not append.
>
> Not in the Elisp sense, no. But in e.g., Python, `append` is the function that's
> used to add an element to a list and the OP indicated that that's what he was
> after.

Hmm, of course you meant "it doesn't add the new element to the end of the
list"... I thought you were referring to the fact that in Elisp, `append`
combines lists into a single list.


-- 
Joost Kremers
Life has its moments

Re: Appending to a list

[steve-humphreys]

> Sent: Sunday, December 13, 2020 at 11:43 PM
> From: "Stefan Monnier" <monnier@iro.umontreal.ca>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> >> `push` is what I would use:
> >>     (push "Swift" bird)
> >
> > This does not append.
> 
> Indeed, and it's a feature: append costs O(n), both in immediate CPU
> time and in memory allocations (which can increase memory use or at
> least increase the time spent in the GC) where `n` is the length of the
> list to which you append.  So if you do that O(n) times, you get an
> overall O(n²) complexity.

I don't care the way I insert.  If inserting in the beginning is more
efficient I would do that..  
 
> IOW, in most cases you're really better off with pushing to the
> beginning of the list, and if the order doesn't suit you, then use
> `reverse` afterwards, which will still be O(n) overall rather than
> O(n²).
> 
> >> No need to use `setq` here.
> >>
> >> `push` won't check if the element is already in the list, though. You can use
> >> `cl-pushnew` in that case, but be sure to load the library it's in:
> >>
> >>     (require 'cl-lib)
> >>     (cl-pushnew "Swift" bird)
> > Isn't that the same as
> > (add-to-list bird "Swift" t)
> 
> Not quite:
> 
> - your `t` at the end makes `add-to-list` add to the rear of the
>   list whereas `cl-pushnew` adds it to the front.
> - `add-to-list` would require you to quote the variable symbol, as in:
> 
>       (add-to-list 'bird "Swift" t)
> 
> - `add-to-list` cannot operate on a lexically scoped `bird` variable.
> 
> - `add-to-list` cannot operate on generalized variables, whereas
>   `cl-pushnew` (just like `push`) will be happy with things like
> 
>       (cl-pushnew "Swift" (gethash "birds" table))
> 
> - `cl-pushnew` by default compares with `eql` whereas here you'd likely
>   want to compare with `equal`, like `add-to-list` does, so you'd need:
> 
>       (cl-pushnew "Swift" bird :test #'equal)
> 
> BTW `push` is significantly faster than either of `add-to-list` or
> `cl-pushnew` since it doesn't need to check in O(n) time if the
> element is already on the list.
 

I am thinking using push if there are only few caveats when using it,
compared to the other ones.
 
>         Stefan
> 
> 
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> Basically I just want to push entries that are themselves
> lists, and just go with push push push ...

You can use `cl-pushnew' for pushing lists as well!

As in:

(require 'cl-lib)

(defvar bird-list-all)
(defvar bird-list-1)
(defvar bird-list-2)

(setq bird-list-all '())

(setq bird-list-1   '("Western jackdaw" "European goldfinch"))
(setq bird-list-2   '("rook"))

(cl-pushnew bird-list-1 bird-list-all) ; (("Western jackdaw" "European goldfinch"))
(cl-pushnew bird-list-2 bird-list-all) ; (("rook") ("Western jackdaw" "European goldfinch"))

Birds and Elisp! That, I didn't see coming!

Check out this file:

  https://dataswamp.org/~incal/BIRDS

It even has some Elisp to compute the number of observed birds
("kryss", as they are called in Swedish). I have 61, that means
not much of an ornithologist, I'm afraid :$

:)

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> I don't care the way I insert. If inserting in the beginning
> is more efficient I would do that

These two sentences are inconsistent :)

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 12:33 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
>
> > I don't care the way I insert. If inserting in the beginning
> > is more efficient I would do that
>
> These two sentences are inconsistent :)

Could have made a good politician then!

I don't mind inserting at the beginning if that makes things more efficient. :)


> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> I don't mind inserting at the beginning if that makes things
> more efficient. :)

In your particular use case it will probably never be an issue
of efficiency but as a programmer I guess the more details you
know and understand and can put to good use the better...

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

Consider I have the following two templates, and want a make a list
named "tmplt-animal", which I can then pass to org-capture-templates.

(setq org-capture-templates tmplt-animal)

How can I use "push" to do that?

-------- template code --------

(setq tmplt-bird `(

("1" "Toucan" entry
(file "~/animal.org")
,(concat
"* Toucan\n"
" Species:\n"
" Region: %?\n"
" Brief:\n"
" Entered: %T\n"))

("2" "King Fisher" entry
(file "~/animal.org")
,(concat
"* King Fisher"
" Species:\n"
" Region: %?\n"
" Brief:\n"
" Entered: %T\n")) ))

(setq tmplt-Amphibian `(

("3" "Frog or Toad" entry
(file "~/animal.org")
,(concat
"* Frog or Toad\n"
" Species:\n"
" Region: %?\n"
" Brief:\n"
" Entered: %T\n"))

("4" "Salamander" entry
(file "~/animal.org")
,(concat
"* King Fisher"
" Species:\n"
" Region: %?\n"
" Brief:\n"
" Entered: %T\n")) ))

> Sent: Monday, December 14, 2020 at 1:37 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
>
> > I don't mind inserting at the beginning if that makes things
> > more efficient. :)
>
> In your particular use case it will probably never be an issue
> of efficiency but as a programmer I guess the more details you
> know and understand and can put to good use the better...
>
> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> (setq tmplt-bird `(
>
> ("1" "Toucan" entry
> (file "~/animal.org")
> ,(concat
> "* Toucan\n"
> " Species:\n"
> " Region: %?\n"
> " Brief:\n"
> " Entered: %T\n")) [...]

Darn, it is epidemic! Now you do that as well! What is that???

While it looks MUCH better than the other guy's it is still all
over the place IMO.

But to answer your question: no idea.

:)

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 3:58 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
>
> > (setq tmplt-bird `(
> >
> > ("1" "Toucan" entry
> > (file "~/animal.org")
> > ,(concat
> > "* Toucan\n"
> > " Species:\n"
> > " Region: %?\n"
> > " Brief:\n"
> > " Entered: %T\n")) [...]
>
> Darn, it is epidemic! Now you do that as well! What is that???

Coronavirus! :)

> While it looks MUCH better than the other guy's it is still all
> over the place IMO.
>
> But to answer your question: no idea.
>
> :)
>
> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>
>

Re: Appending to a list

[Michael Heerdegen]

steve-humphreys@gmx.com writes:

> Consider I have the following two templates, and want a make a list
> named "tmplt-animal", which I can then pass to org-capture-templates.
>
> (setq org-capture-templates tmplt-animal)
>
> How can I use "push" to do that?
>
> -------- template code --------
> [...]

Seems your list is actually not an element to add that just happens to
be a list, but a list of elements you want to add (but the elements are
also lists again, ehem...)

In this case you want to `append' the lists, not `push'.  You may also
define those bindings using `defvar' if you really want to set all the
used variables at top level.


Michael.

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

Michael Heerdegen wrote:

> In this case you want to `append' the lists, not `push'.
> You may also define those bindings using `defvar' if you
> really want to set all the used variables at top level.

... and to shut up the byte compiler :)

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 5:07 AM
> From: "Michael Heerdegen" <michael_heerdegen@web.de>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys@gmx.com writes:
>
> > Consider I have the following two templates, and want a make a list
> > named "tmplt-animal", which I can then pass to org-capture-templates.
> >
> > (setq org-capture-templates tmplt-animal)
> >
> > How can I use "push" to do that?
> >
> > -------- template code --------
> > [...]
>
> Seems your list is actually not an element to add that just happens to
> be a list, but a list of elements you want to add (but the elements are
> also lists again, ehem...)

I thought I could push element by element.

> In this case you want to `append' the lists, not `push'.  You may also
> define those bindings using `defvar' if you really want to set all the
> used variables at top level.

I got inspiration from some discussions here that push is more efficient
and wanted to have a go.  Yes, I do use push to make the larger list.
Have not thought about defvar before.  I have read that "setq" does not
introduce a variable, but I would need some explanation about that.

> Michael.
>
>
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> I thought I could push element by element.

You can, you can push whatever, if that data structure makes it
more involved solve it for onee pilot case, then write a small
`defun', put it there, and ever after just pass the single
element to that.

> I got inspiration from some discussions here that push is
> more efficient and wanted to have a go. Yes, I do use push to
> make the larger list. Have not thought about defvar before.
> I have read that "setq" does not introduce a variable, but
> I would need some explanation about that.

It works with `setq' only without `defvar' the byte-compiler,
which should always be used BTW, without it the byte-compiler
will complain.

Comment-out the defvars in this

(require 'cl-lib)

(defvar bird-list-all)
(defvar bird-list-1)
(defvar bird-list-2)

(setq bird-list-all '())

(setq bird-list-1   '("Western jackdaw" "European goldfinch"))
(setq bird-list-2   '("rook"))

(cl-pushnew bird-list-1 bird-list-all) ; (("Western jackdaw" "European goldfinch"))
(cl-pushnew bird-list-2 bird-list-all) ; (("rook") ("Western jackdaw" "European goldfinch"))

and the byte-compiler will say

  geh.el: 
  In toplevel form:
  geh.el:193:7: Warning: assignment to free variable ‘bird-list-all’
  geh.el:195:7: Warning: assignment to free variable ‘bird-list-1’
  geh.el:196:7: Warning: assignment to free variable ‘bird-list-2’
  geh.el:198:13: Warning: reference to free variable ‘bird-list-1’
  geh.el:198:25: Warning: reference to free variable ‘bird-list-all’
  geh.el:199:13: Warning: reference to free variable ‘bird-list-2’

In more ambitious projects, like a package, e.g. [1], defvar
should be used also to make available documentation, both in
the code and for the on-line help which in practice is the same
thing - Emacs is self-documenting, remember?

Heh, not really, right? But still, do it.

Anyway, don't rely too much on variables, defvar or no defvar.
Better to rely on defuns and use `let' and `let*' there. IMO!

[1] https://dataswamp.org/~incal/emacs-init/buc.el

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 5:50 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
> 
> > I thought I could push element by element.
> 
> You can, you can push whatever, if that data structure makes it
> more involved solve it for onee pilot case, then write a small
> `defun', put it there, and ever after just pass the single
> element to that.
> 
> > I got inspiration from some discussions here that push is
> > more efficient and wanted to have a go. Yes, I do use push to
> > make the larger list. Have not thought about defvar before.
> > I have read that "setq" does not introduce a variable, but
> > I would need some explanation about that.
> 
> It works with `setq' only without `defvar' the byte-compiler,
> which should always be used BTW, without it the byte-compiler
> will complain.
> 
> Comment-out the defvars in this
> 
> (require 'cl-lib)
> 
> (defvar bird-list-all)
> (defvar bird-list-1)
> (defvar bird-list-2)
> 
> (setq bird-list-all '())
> 
> (setq bird-list-1   '("Western jackdaw" "European goldfinch"))
> (setq bird-list-2   '("rook"))
> 
> (cl-pushnew bird-list-1 bird-list-all) ; (("Western jackdaw" "European goldfinch"))
> (cl-pushnew bird-list-2 bird-list-all) ; (("rook") ("Western jackdaw" "European goldfinch"))
> 
> and the byte-compiler will say
> 
>   geh.el: 
>   In toplevel form:
>   geh.el:193:7: Warning: assignment to free variable ‘bird-list-all’
>   geh.el:195:7: Warning: assignment to free variable ‘bird-list-1’
>   geh.el:196:7: Warning: assignment to free variable ‘bird-list-2’
>   geh.el:198:13: Warning: reference to free variable ‘bird-list-1’
>   geh.el:198:25: Warning: reference to free variable ‘bird-list-all’
>   geh.el:199:13: Warning: reference to free variable ‘bird-list-2’
> 
> In more ambitious projects, like a package, e.g. [1], defvar
> should be used also to make available documentation, both in
> the code and for the on-line help which in practice is the same
> thing - Emacs is self-documenting, remember?
> 
> Heh, not really, right? But still, do it.
> 
> Anyway, don't rely too much on variables, defvar or no defvar.
> Better to rely on defuns and use `let' and `let*' there. IMO!

Yes, I have used "let" and "let*" to take a word and make frog
over other words. 
 
> [1] https://dataswamp.org/~incal/emacs-init/buc.el
> 
> -- 
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
> 
> 
>

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 5:50 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
> 
> > I thought I could push element by element.
> 
> You can, you can push whatever, if that data structure makes it
> more involved solve it for onee pilot case, then write a small
> `defun', put it there, and ever after just pass the single
> element to that.
> 
> > I got inspiration from some discussions here that push is
> > more efficient and wanted to have a go. Yes, I do use push to
> > make the larger list. Have not thought about defvar before.
> > I have read that "setq" does not introduce a variable, but
> > I would need some explanation about that.
> 
> It works with `setq' only without `defvar' the byte-compiler,
> which should always be used BTW, without it the byte-compiler
> will complain.

I have not understood the paragraph above.

> Comment-out the defvars in this
> 
> (require 'cl-lib)
> 
> (defvar bird-list-all)
> (defvar bird-list-1)
> (defvar bird-list-2)
> 
> (setq bird-list-all '())
> 
> (setq bird-list-1   '("Western jackdaw" "European goldfinch"))
> (setq bird-list-2   '("rook"))
> 
> (cl-pushnew bird-list-1 bird-list-all) ; (("Western jackdaw" "European goldfinch"))
> (cl-pushnew bird-list-2 bird-list-all) ; (("rook") ("Western jackdaw" "European goldfinch"))
> 
> and the byte-compiler will say
> 
>   geh.el: 
>   In toplevel form:
>   geh.el:193:7: Warning: assignment to free variable ‘bird-list-all’
>   geh.el:195:7: Warning: assignment to free variable ‘bird-list-1’
>   geh.el:196:7: Warning: assignment to free variable ‘bird-list-2’
>   geh.el:198:13: Warning: reference to free variable ‘bird-list-1’
>   geh.el:198:25: Warning: reference to free variable ‘bird-list-all’
>   geh.el:199:13: Warning: reference to free variable ‘bird-list-2’
> 
> In more ambitious projects, like a package, e.g. [1], defvar
> should be used also to make available documentation, both in
> the code and for the on-line help which in practice is the same
> thing - Emacs is self-documenting, remember?
> 
> Heh, not really, right? But still, do it.
> 
> Anyway, don't rely too much on variables, defvar or no defvar.
> Better to rely on defuns and use `let' and `let*' there. IMO!
> 
> [1] https://dataswamp.org/~incal/emacs-init/buc.el
> 
> -- 
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
> 
> 
>

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 5:50 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
> 
> > I thought I could push element by element.
> 
> You can, you can push whatever, if that data structure makes it
> more involved solve it for onee pilot case, then write a small
> `defun', put it there, and ever after just pass the single
> element to that.
> 
> > I got inspiration from some discussions here that push is
> > more efficient and wanted to have a go. Yes, I do use push to
> > make the larger list. Have not thought about defvar before.
> > I have read that "setq" does not introduce a variable, but
> > I would need some explanation about that.
> 
> It works with `setq' only without `defvar' the byte-compiler,
> which should always be used BTW, without it the byte-compiler
> will complain.

Do you mean that by commenting the defvars and using "setq",
the compiler will complain because no variables were defined
by bird-list*.  

defvar can only be assigned if they have not been set and have
a documentation string.  But when do you decide betweenh setq 
and defvar?
 
> Comment-out the defvars in this
> 
> (require 'cl-lib)
> 
> (defvar bird-list-all)
> (defvar bird-list-1)
> (defvar bird-list-2)
> 
> (setq bird-list-all '())
> 
> (setq bird-list-1   '("Western jackdaw" "European goldfinch"))
> (setq bird-list-2   '("rook"))
> 
> (cl-pushnew bird-list-1 bird-list-all) ; (("Western jackdaw" "European goldfinch"))
> (cl-pushnew bird-list-2 bird-list-all) ; (("rook") ("Western jackdaw" "European goldfinch"))

Is the problem with the compiler occurring because of cl-pushnew?
 
> and the byte-compiler will say
> 
>   geh.el: 
>   In toplevel form:
>   geh.el:193:7: Warning: assignment to free variable ‘bird-list-all’
>   geh.el:195:7: Warning: assignment to free variable ‘bird-list-1’
>   geh.el:196:7: Warning: assignment to free variable ‘bird-list-2’
>   geh.el:198:13: Warning: reference to free variable ‘bird-list-1’
>   geh.el:198:25: Warning: reference to free variable ‘bird-list-all’
>   geh.el:199:13: Warning: reference to free variable ‘bird-list-2’
> 
> In more ambitious projects, like a package, e.g. [1], defvar
> should be used also to make available documentation, both in
> the code and for the on-line help which in practice is the same
> thing - Emacs is self-documenting, remember?
> 
> Heh, not really, right? But still, do it.
> 
> Anyway, don't rely too much on variables, defvar or no defvar.
> Better to rely on defuns and use `let' and `let*' there. IMO!
> 
> [1] https://dataswamp.org/~incal/emacs-init/buc.el
> 
> -- 
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
> 
> 
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> Yes, I have used "let" and "let*" to take a word and make
> frog over other words.

?

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 7:20 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
>
> > Yes, I have used "let" and "let*" to take a word and make
> > frog over other words.

Made a defun to skip over words, and used let.  Jump over words
like a frog.

> ?
>
> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

>> It works with `setq' only without `defvar' the
>> byte-compiler, which should always be used BTW, without it
>> the byte-compiler will complain.
>
> I have not understood the paragraph above.

After you have written some Elisp, say fort-knox-access.el, use
the byte-compiler like this

  $ emacs -batch -f batch-byte-compile fort-knox-access.el

The byte-compiler will tell you how to improve your code and
also when the output fort-knox-access.elc file is loaded in
Emacs it will run faster to some extent.

--
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> Do you mean that by commenting the defvars and using "setq",
> the compiler will complain because no variables were defined
> by bird-list*.

Yes, removing or commenting out the defvars and then using
`setq' that will happen.

> defvar can only be assigned if they have not been set and
> have a documentation string.

Use `defvar' before setq. The init value is often a source of
confusion... but use it by all means if it fancies you.
The docstring is also optional. Use it in packages. In your own
code, obviously you do whatever you want.

Just

  (defvar pi)
  (setq pi 3.1415)

is OK :)

> But when do you decide betweenh setq and defvar?

Use defvar first, then setq. But avoid it all if you can by
using defuns and `let'/`let*'.

> Is the problem with the compiler occurring because of
> cl-pushnew?

The byte-compiler is OK with `cl-pushnew' because of the
previous (require 'cl-lib) line.

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 7:26 AM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> steve-humphreys wrote:
>
> >> It works with `setq' only without `defvar' the
> >> byte-compiler, which should always be used BTW, without it
> >> the byte-compiler will complain.
> >
> > I have not understood the paragraph above.
>
> After you have written some Elisp, say fort-knox-access.el, use
> the byte-compiler like this
>
>   $ emacs -batch -f batch-byte-compile fort-knox-access.el
>
> The byte-compiler will tell you how to improve your code and
> also when the output fort-knox-access.elc file is loaded in
> Emacs it will run faster to some extent.

I see.

> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>
>

Re: Appending to a list

[Michael Heerdegen]

steve-humphreys@gmx.com writes:

> > Seems your list is actually not an element to add that just happens to
> > be a list, but a list of elements you want to add (but the elements are
> > also lists again, ehem...)
>
> I thought I could push element by element.

Seems there is/was a misunderstanding: that you wanted to append an
one-element list, which is apparently not the case.  In the general
case, `append' is of course not less efficient than pushing from one
list to another element by element.

Regards,

Michael.

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

Michael Heerdegen wrote:

> Seems there is/was a misunderstanding: that you wanted to
> append an one-element list, which is apparently not the case.
> In the general case, `append' is of course not less efficient
> than pushing from one list to another element by element.

I don't understand the issue, even less than you because
I don't even understand it enough to misunderstand it, _but_
I think the focus should be how to just solve it using standard
and common methods, they will be efficient enough :)

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal

Re: Appending to a list

[steve-humphreys]

> Sent: Monday, December 14, 2020 at 7:25 PM
> From: "Emanuel Berg via Users list for the GNU Emacs text editor" <help-gnu-emacs@gnu.org>
> To: help-gnu-emacs@gnu.org
> Subject: Re: Appending to a list
>
> Michael Heerdegen wrote:
>
> > Seems there is/was a misunderstanding: that you wanted to
> > append an one-element list, which is apparently not the case.
> > In the general case, `append' is of course not less efficient
> > than pushing from one list to another element by element.
>
> I don't understand the issue, even less than you because
> I don't even understand it enough to misunderstand it, _but_
> I think the focus should be how to just solve it using standard
> and common methods, they will be efficient enough :)

I got greedy.

> --
> underground experts united
> http://user.it.uu.se/~embe8573
> https://dataswamp.org/~incal
>
>
>

Re: Appending to a list

[Emanuel Berg via Users list for the GNU Emacs text editor]

steve-humphreys wrote:

> I got greedy.

Greedy algorithm: at every step of the way, choose the most
rewarding next step.

Usually works well but without the big picture it can lead to
dead ends.

But a good bet if you don't know what else to do.

-- 
underground experts united
http://user.it.uu.se/~embe8573
https://dataswamp.org/~incal