Locating file via load-path

Locating file via load-path

[Heime]

Is this the way to see if a file is accessible via load-path ?
Or do I need 'load-path or similar ?

(if (locate-file "tema.el" load-path)



Sent with Proton Mail secure email.

Re: Locating file via load-path

[Eli Zaretskii]

> Date: Thu, 08 Aug 2024 16:59:04 +0000
> From: Heime <heimeborgia@protonmail.com>
> 
> 
> Is this the way to see if a file is accessible via load-path ?
> Or do I need 'load-path or similar ?
> 
> (if (locate-file "tema.el" load-path)

For ELisp files on load-path, it is better to use locate-library.

Re: Locating file via load-path

[Heime]

Sent with Proton Mail secure email.

On Friday, August 9th, 2024 at 6:33 AM, Eli Zaretskii <eliz@gnu.org> wrote:

> > Date: Thu, 08 Aug 2024 16:59:04 +0000
> > From: Heime heimeborgia@protonmail.com
> > 
> > Is this the way to see if a file is accessible via load-path ?
> > Or do I need 'load-path or similar ?
> > 
> > (if (locate-file "tema.el" load-path)
> 
> 
> For ELisp files on load-path, it is better to use locate-library.

Would the check for a general file prevodilac.el be this ?

(locate-library "prevodilac") 

Re: Locating file via load-path

[Heime]

On Friday, August 9th, 2024 at 7:09 AM, Heime <heimeborgia@protonmail.com> wrote:

> Sent with Proton Mail secure email.
> 
> On Friday, August 9th, 2024 at 6:33 AM, Eli Zaretskii eliz@gnu.org wrote:
> 
> > > Date: Thu, 08 Aug 2024 16:59:04 +0000
> > > From: Heime heimeborgia@protonmail.com
> > > 
> > > Is this the way to see if a file is accessible via load-path ?
> > > Or do I need 'load-path or similar ?
> > > 
> > > (if (locate-file "tema.el" load-path)
> > 
> > For ELisp files on load-path, it is better to use locate-library.
> 
> 
> Would the check for a general file prevodilac.el be this ?
> 
> (locate-library "prevodilac")

How can different files under different paths but having the same name be handled ?

Re: Locating file via load-path

[Heime]

Sent with Proton Mail secure email.

On Friday, August 9th, 2024 at 7:15 AM, Heime <heimeborgia@protonmail.com> wrote:

> On Friday, August 9th, 2024 at 7:09 AM, Heime heimeborgia@protonmail.com wrote:
> 
> > Sent with Proton Mail secure email.
> > 
> > On Friday, August 9th, 2024 at 6:33 AM, Eli Zaretskii eliz@gnu.org wrote:
> > 
> > > > Date: Thu, 08 Aug 2024 16:59:04 +0000
> > > > From: Heime heimeborgia@protonmail.com
> > > > 
> > > > Is this the way to see if a file is accessible via load-path ?
> > > > Or do I need 'load-path or similar ?
> > > > 
> > > > (if (locate-file "tema.el" load-path)
> > > 
> > > For ELisp files on load-path, it is better to use locate-library.
> > 
> > Would the check for a general file prevodilac.el be this ?
> > 
> > (locate-library "prevodilac")
> 
> 
> How can different files under different paths but having the same name be handled ?

What I want to do is this.

Should package-path not has been added to load-path using

(add-to-list 'load-path package-path)

then a test is made, so it is added if required

 (if (locate-file "tema.el" load-path)
    (require 'tema)
   (progn
     (add-to-list 'load-path tema-path)
     (require 'tema)))

RE: [External] : Re: Locating file via load-path

[Drew Adams]

> a test is made, so it is added if required
> 
>  (if (locate-file "tema.el" load-path)
>     (require 'tema)

(require 'tema nil t)
loads it if available, and returns nil otherwise.

>    (progn
>      (add-to-list 'load-path tema-path)
>      (require 'tema)))

You might as well just add it to `load-path'
unconditionally, unless it's already there:

(cl-pushnew tema load-path)

RE: [External] : Re: Locating file via load-path

[Heime]

Sent with Proton Mail secure email.

On Friday, August 9th, 2024 at 7:51 AM, Drew Adams <drew.adams@oracle.com> wrote:

> > a test is made, so it is added if required
> > 
> > (if (locate-file "tema.el" load-path)
> > (require 'tema)
> 
> 
> (require 'tema nil t)
> loads it if available, and returns nil otherwise.
> 
> > (progn
> > (add-to-list 'load-path tema-path)
> > (require 'tema)))
> 
> 
> You might as well just add it to `load-path'
> unconditionally, unless it's already there:
> 
> (cl-pushnew tema load-path)

That would be a good thing.  

(add-to-list 'load-path tema-path) should add tema-path only if it isn't 
there yet.  Why cl-pushnew ?

RE: [External] : Re: Locating file via load-path

[Drew Adams]

> On Friday, August 9th, 2024 at 7:51 AM, Drew Adams wrote:
> 
> > > a test is made, so it is added if required
> > >
> > > (if (locate-file "tema.el" load-path)
> > > (require 'tema)
> >
> >
> > (require 'tema nil t)
> > loads it if available, and returns nil otherwise.
> >
> > > (progn
> > > (add-to-list 'load-path tema-path)
> > > (require 'tema)))
> >
> > You might as well just add it to `load-path'
> > unconditionally, unless it's already there:
> >
> > (cl-pushnew tema load-path)

(I meant tema-path, not tema.)

> That would be a good thing.
> 
> (add-to-list 'load-path tema-path) should add tema-path only if it isn't
> there yet.  Why cl-pushnew ?

Either is OK.  The doc of `add-to-list' says:

  you are usually better off using `push' or `cl-pushnew'.

It doesn't say why, and neither does the Elisp manual.

Some people get confused over the args to `add-to-list',
in particular, that it's a function, so it evaluates its
args, so if you want to provide a variable literally
then you need to quote it.

RE: [External] : Re: Locating file via load-path

[Heime]

On Friday, August 9th, 2024 at 9:25 AM, Drew Adams <drew.adams@oracle.com> wrote:

> > On Friday, August 9th, 2024 at 7:51 AM, Drew Adams wrote:
> > 
> > > > a test is made, so it is added if required
> > > > 
> > > > (if (locate-file "tema.el" load-path)
> > > > (require 'tema)
> > > 
> > > (require 'tema nil t)
> > > loads it if available, and returns nil otherwise.
> > > 
> > > > (progn
> > > > (add-to-list 'load-path tema-path)
> > > > (require 'tema)))
> > > 
> > > You might as well just add it to `load-path'
> > > unconditionally, unless it's already there:
> > > 
> > > (cl-pushnew tema load-path)
> 
> 
> (I meant tema-path, not tema.)
> 
> > That would be a good thing.
> > 
> > (add-to-list 'load-path tema-path) should add tema-path only if it isn't
> > there yet. Why cl-pushnew ?
> 
> 
> Either is OK. The doc of `add-to-list' says: you are usually better off using` push' or `cl-pushnew'. It doesn't say why, and neither does the Elisp manual. Some people get confused over the args to` add-to-list',
> in particular, that it's a function, so it evaluates its
> args, so if you want to provide a variable literally
> then you need to quote it.

Are you referring to quoting LIST-VAR ? add-to-list expects the first 
argument to be the symbol of a list variable, not the list itself.

RE: [External] : Re: Locating file via load-path

[Drew Adams]

> > Some people get confused over the args to` add-to-list',
> > in particular, that it's a function, so it evaluates its
> > args, so if you want to provide a variable literally
> > then you need to quote it.
> 
> Are you referring to quoting LIST-VAR ?

Yes.

> add-to-list expects the first argument to be the
> symbol of a list variable, not the list itself.

Yes.

Which is why, if you want to pass a variable's
symbol literally, you need to quote it: 'SYMBOL
evals to SYMBOL.

Arg LIST-VAR in code can be any sexp.  It need not
be something as obvious as 'var.

RE: [External] : Re: Locating file via load-path

[Heime]

Sent with Proton Mail secure email.

On Friday, August 9th, 2024 at 10:30 AM, Drew Adams <drew.adams@oracle.com> wrote:

> > > Some people get confused over the args to` add-to-list',
> > > in particular, that it's a function, so it evaluates its
> > > args, so if you want to provide a variable literally
> > > then you need to quote it.
> > 
> > Are you referring to quoting LIST-VAR ?
> 
> 
> Yes.
> 
> > add-to-list expects the first argument to be the
> > symbol of a list variable, not the list itself.
> 
> 
> Yes.
> 
> Which is why, if you want to pass a variable's
> symbol literally, you need to quote it: 'SYMBOL
> evals to SYMBOL.
> 
> Arg LIST-VAR in code can be any sexp. It need not
> be something as obvious as 'var.

There should not be the problem you mention for the case of load-path
because all instances show that it is customarily quoted.

Re: [External] : Re: Locating file via load-path

[Eli Zaretskii]

> From: Drew Adams <drew.adams@oracle.com>
> CC: Eli Zaretskii <eliz@gnu.org>,
>         "help-gnu-emacs@gnu.org"
> 	<help-gnu-emacs@gnu.org>
> Date: Thu, 8 Aug 2024 21:25:46 +0000
> 
> > (add-to-list 'load-path tema-path) should add tema-path only if it isn't
> > there yet.  Why cl-pushnew ?
> 
> Either is OK.  The doc of `add-to-list' says:
> 
>   you are usually better off using `push' or `cl-pushnew'.

Talk about citation out of context.  The full quotation is

  This is handy to add some elements to configuration variables,
  but please do not abuse it in Elisp code, where you are usually
  better off using ‘push’ or ‘cl-pushnew’.

IOW, don't (ab)use add-to-list if all you need is to add a new element
to some list of elements.  add-to-list is for adding path elements to
variables like load-path.

> It doesn't say why, and neither does the Elisp manual.

Oh, yes, it does, see above.

RE: [External] : Re: Locating file via load-path

[Drew Adams]

> > > Why cl-pushnew ?
> >
> > Either is OK.  The doc of `add-to-list' says:
> >
> >   you are usually better off using `push' or `cl-pushnew'.
> 
> Talk about citation out of context.  The full quotation is
> 
>   This is handy to add some elements to configuration variables,
>   but please do not abuse it in Elisp code, where you are usually
>   better off using ‘push’ or ‘cl-pushnew’.
> 
> IOW, don't (ab)use add-to-list if all you need is to add a new element
> to some list of elements.  add-to-list is for adding path elements to
> variables like load-path.

That text says use it mainly for user ("configuration")
variables, not generally for Lisp code.  And it neither
says nor suggests anything about lists of path elements.

> > It doesn't say why, and neither does the Elisp manual.
> 
> Oh, yes, it does, see above.

No, there's nothing about "why" above.

May I humbly encourage you to review the following
mails in this very list from Stefan Monnier on the
subject, back in 2013, during his tenure as the
Emacs maintainer (thread "Is add-to-list supposed
to work when lexical-binding is t?"):

Not in chronological order, but perhaps in order of
relevance and understanding for us, here:

https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00096.html

https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00064.html

https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00124.html

https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00188.html

In particular, this bit summarizes _WHY_ he added that
"usually better off using ‘push’ or ‘cl-pushnew’" [in
Lisp code] text to the doc string (in Emacs 24):

  "The warning was added because add-to-list is a
   frequent use-case where Elisp code presumes
   dynamic binding."

And:

  > Unless you're knee-deep in the internals of the language,
  > the difference between `cl-pushnew' and `add-to-list' is
  > so obscure as to be incomprehensible.

  "Agreed.  I never liked add-to-list, and now I really
   know why ... other than by ad-hoc handling the case
   where the first arg is passed via quoting, the
   byte-compiler" [is pretty hopeless for add-to-list]

Locating file via load-path

[Christopher Dimech]

> Sent: Saturday, August 10, 2024 at 4:19 AM
> From: "Drew Adams" <drew.adams@oracle.com>
> To: "Eli Zaretskii" <eliz@gnu.org>, "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
> Subject: RE: [External] : Re: Locating file via load-path
>
> > > > Why cl-pushnew ?
> > >
> > > Either is OK.  The doc of `add-to-list' says:
> > >
> > >   you are usually better off using `push' or `cl-pushnew'.
> > 
> > Talk about citation out of context.  The full quotation is
> > 
> >   This is handy to add some elements to configuration variables,
> >   but please do not abuse it in Elisp code, where you are usually
> >   better off using ‘push’ or ‘cl-pushnew’.
> > 
> > IOW, don't (ab)use add-to-list if all you need is to add a new element
> > to some list of elements.  add-to-list is for adding path elements to
> > variables like load-path.
> 
> That text says use it mainly for user ("configuration")
> variables, not generally for Lisp code.  And it neither
> says nor suggests anything about lists of path elements.
> 
> > > It doesn't say why, and neither does the Elisp manual.
> > 
> > Oh, yes, it does, see above.
> 
> No, there's nothing about "why" above.
> 
> May I humbly encourage you to review the following
> mails in this very list from Stefan Monnier on the
> subject, back in 2013, during his tenure as the
> Emacs maintainer (thread "Is add-to-list supposed
> to work when lexical-binding is t?"):

In such case add-to-list has to the potential for misleading code.
There’s an argument to be made that functions like add-to-list 
should be robust enough to handle a variety of scenarios, not just
for modifying configuration variables like load-path.  There should 
be some robustness expectations rather than expecting users not to 
abuse it.  The function should be versatile and resistant to misuse.

If developers could use more appropriate list operations when dealing 
with general-purpose list manipulation (including for load-path), the
better life would be for everybody. 

> Not in chronological order, but perhaps in order of
> relevance and understanding for us, here:
> 
> https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00096.html
> 
> https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00064.html
> 
> https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00124.html
> 
> https://mail.gnu.org/archive/html/help-gnu-emacs/2013-06/msg00188.html
> 
> In particular, this bit summarizes _WHY_ he added that
> "usually better off using ‘push’ or ‘cl-pushnew’" [in
> Lisp code] text to the doc string (in Emacs 24):
> 
>   "The warning was added because add-to-list is a
>    frequent use-case where Elisp code presumes
>    dynamic binding."
> 
> And:
> 
>   > Unless you're knee-deep in the internals of the language,
>   > the difference between `cl-pushnew' and `add-to-list' is
>   > so obscure as to be incomprehensible.
> 
>   "Agreed.  I never liked add-to-list, and now I really
>    know why ... other than by ad-hoc handling the case
>    where the first arg is passed via quoting, the
>    byte-compiler" [is pretty hopeless for add-to-list]
> 
>

Re: [External] : Re: Locating file via load-path

[Eli Zaretskii]

> From: Drew Adams <drew.adams@oracle.com>
> Date: Fri, 9 Aug 2024 16:19:01 +0000
> 
> > > > Why cl-pushnew ?
> > >
> > > Either is OK.  The doc of `add-to-list' says:
> > >
> > >   you are usually better off using `push' or `cl-pushnew'.
> > 
> > Talk about citation out of context.  The full quotation is
> > 
> >   This is handy to add some elements to configuration variables,
> >   but please do not abuse it in Elisp code, where you are usually
> >   better off using ‘push’ or ‘cl-pushnew’.
> > 
> > IOW, don't (ab)use add-to-list if all you need is to add a new element
> > to some list of elements.  add-to-list is for adding path elements to
> > variables like load-path.
> 
> That text says use it mainly for user ("configuration")
> variables, not generally for Lisp code.  And it neither
> says nor suggests anything about lists of path elements.

It did, albeit not explicitly enough.  Now it does that more clearly.

> > > It doesn't say why, and neither does the Elisp manual.
> > 
> > Oh, yes, it does, see above.
> 
> No, there's nothing about "why" above.

Only if you refuse to think about what it says.

> May I humbly encourage you to review the following
> mails in this very list from Stefan Monnier on the
> subject, back in 2013, during his tenure as the
> Emacs maintainer (thread "Is add-to-list supposed
> to work when lexical-binding is t?"):
> 
> Not in chronological order, but perhaps in order of
> relevance and understanding for us, here:

Not relevant to this discussion.

Re: Locating file via load-path

[Arash Esbati]

Eli Zaretskii <eliz@gnu.org> writes:

>   This is handy to add some elements to configuration variables,
>   but please do not abuse it in Elisp code, where you are usually
>   better off using ‘push’ or ‘cl-pushnew’.
>
> IOW, don't (ab)use add-to-list if all you need is to add a new element
> to some list of elements.

Maybe off-topic, but I always missed the APPEND arg provided by
`add-to-list' in `cl-pushnew'.

Best, Arash

Re: Locating file via load-path

[Eli Zaretskii]

> From: Arash Esbati <arash@gnu.org>
> Cc: help-gnu-emacs@gnu.org
> Date: Fri, 09 Aug 2024 21:52:24 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >   This is handy to add some elements to configuration variables,
> >   but please do not abuse it in Elisp code, where you are usually
> >   better off using ‘push’ or ‘cl-pushnew’.
> >
> > IOW, don't (ab)use add-to-list if all you need is to add a new element
> > to some list of elements.
> 
> Maybe off-topic, but I always missed the APPEND arg provided by
> `add-to-list' in `cl-pushnew'.

If the order matters, then perhaps cl-pushnew is not what you want.
Or maybe you need to sort the list in some way.

The order rarely matters if all you need is to construct a list of
arbitrary elements.

Re: Locating file via load-path

[Arash Esbati]

Eli Zaretskii <eliz@gnu.org> writes:

> If the order matters, then perhaps cl-pushnew is not what you want.

And then I usually end up using `add-to-list'.  Admittedly, it is not
often, but sometimes I need to append an entry to a list from lisp, and
this missing bit keeps me from using `cl-pushnew' exclusively.

Best, Arash

Re: Locating file via load-path

[Eli Zaretskii]

> From: Arash Esbati <arash@gnu.org>
> Cc: help-gnu-emacs@gnu.org
> Date: Sun, 11 Aug 2024 15:35:05 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > If the order matters, then perhaps cl-pushnew is not what you want.
> 
> And then I usually end up using `add-to-list'.

Why not nconc?

Re: Locating file via load-path

[Arash Esbati]

Eli Zaretskii <eliz@gnu.org> writes:

> Why not nconc?

The use case I have to deal with runs inside hooks which run more than
once, and I don't want to pollute the target variable with same entry
over and over again.

Of course I can check if the entry is already there, but I think it
would be convenient if `cl-pushnew' could be a full replacement for
`add-to-list' and one would use only the former in Lisp and be done with
it.

Best, Arash

RE: [External] : Re: Locating file via load-path

[Drew Adams]

> > Why not nconc?
> 
> The use case I have to deal with runs inside hooks which run more than
> once, and I don't want to pollute the target variable with same entry
> over and over again.
> 
> Of course I can check if the entry is already there, but I think it
> would be convenient if `cl-pushnew' could be a full replacement for
> `add-to-list' and one would use only the former in Lisp and be done with
> it.

It would be OK for Emacs to have such a function,
but it shouldn't be called `cl-pushnew'.

That name should be reserved for our emulation of
the Common Lisp function `pushnew'.  `cl-pushnew'
shouldn't do anything different from what CL's
`pushnew' does.

Just one opinion.

Locating file via load-path

[Christopher Dimech]

> Sent: Monday, August 12, 2024 at 9:07 AM
> From: "Drew Adams" <drew.adams@oracle.com>
> To: "Arash Esbati" <arash@gnu.org>, "Eli Zaretskii" <eliz@gnu.org>
> Cc: "help-gnu-emacs@gnu.org" <help-gnu-emacs@gnu.org>
> Subject: RE: [External] : Re: Locating file via load-path
>
> > > Why not nconc?
> >
> > The use case I have to deal with runs inside hooks which run more than
> > once, and I don't want to pollute the target variable with same entry
> > over and over again.
> >
> > Of course I can check if the entry is already there, but I think it
> > would be convenient if `cl-pushnew' could be a full replacement for
> > `add-to-list' and one would use only the former in Lisp and be done with
> > it.
>
> It would be OK for Emacs to have such a function,
> but it shouldn't be called `cl-pushnew'.
>
> That name should be reserved for our emulation of
> the Common Lisp function `pushnew'.  `cl-pushnew'
> shouldn't do anything different from what CL's
> `pushnew' does.
>
> Just one opinion.

A agree with it.  A good set that are always recommended
would be a great improvement and no guesswork would be
required on which ones are to be used. There could also
be some special ones if properly named.

Re: [External] : Re: Locating file via load-path

[Eli Zaretskii]

> From: Drew Adams <drew.adams@oracle.com>
> CC: Eli Zaretskii <eliz@gnu.org>,
>         "help-gnu-emacs@gnu.org"
> 	<help-gnu-emacs@gnu.org>
> Date: Thu, 8 Aug 2024 19:51:41 +0000
> 
> You might as well just add it to `load-path'
> unconditionally, unless it's already there:
> 
> (cl-pushnew tema load-path)

add-to-list does the same job and doesn't require cl-lib.

Re: Locating file via load-path

[Eli Zaretskii]

> Date: Thu, 08 Aug 2024 19:15:29 +0000
> From: Heime <heimeborgia@protonmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>, help-gnu-emacs@gnu.org
> 
> > Would the check for a general file prevodilac.el be this ?
> > 
> > (locate-library "prevodilac")
> 
> How can different files under different paths but having the same name be handled ?

Why is it important?  And what do you mean by "handled"?

Re: Locating file via load-path

[Eli Zaretskii]

> Date: Thu, 08 Aug 2024 19:09:58 +0000
> From: Heime <heimeborgia@protonmail.com>
> Cc: help-gnu-emacs@gnu.org
> 
> > For ELisp files on load-path, it is better to use locate-library.
> 
> Would the check for a general file prevodilac.el be this ?
> 
> (locate-library "prevodilac") 

The answer is in the doc string of locate-library, I suggest to read
it.

Re: Locating file via load-path

[Bruno Barbier]

Heime <heimeborgia@protonmail.com> writes:

> Is this the way to see if a file is accessible via load-path ?
> Or do I need 'load-path or similar ?
>
> (if (locate-file "tema.el" load-path)

Maybe.

But 'load-path' is for libraries.

Its documentation refers to the info node
   (info "(elisp)Library Search")

and that info node documents 'locate-library'.

So, maybe, depending on your goal, 'locate-library' is more appropriate.

Note that, from the description of 'locate-library', you can jump to its
source code, and, thus see how it's implemented relying on
'locate-file'.

HTH,

Bruno