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Re: [O] Difference :header-args: and :header-args+:?

From: Rainer M Krug
Subject: Re: [O] Difference :header-args: and :header-args+:?
Date: Tue, 09 Sep 2014 10:20:56 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (darwin)

Aaron Ecay <address@hidden> writes:

> Hi Achim,
> 2014ko irailak 8an, Achim Gratz-ek idatzi zuen:
>> Aaron Ecay writes:
>>> Eric Schulte has said <http://mid.gmane.org/address@hidden>
>>> that the deprecation of this feature is “premature”.  I didn’t realize
>>> at the time that the deprecation was also included in the manual rather
>>> than just a code comment.  Possibly it should be un-deprecated.
>> It shouldn't, owing to a number of essentially un-fixable corner cases
>> and its inherent non-scaleability.

I think that one main confusion comes fro the fact that by the new
syntax, the previous properties in the header arguments have been
demoted to sub-properties of the real property :header-args. So all
operations on :header-args are operations on a *set of properties*. If
this is the case, I would opt, in addition to the + operator, to have
a - operator, which *removes* properties from the property set

I would actually call the + an "operation on an already defined
property" and it should give an error message if the property is not set

So we have a property setter (:header-args) and property operators
(header-args+) as well as (hopefully) :header-args-. By using this
terminology, and that the property operators can only be called when the
property has already been defined (which it usually is due to default
values), the usage should be clearer.

The same should apply to the :var as it also contains a set of entities.

> Can you say more about the corner cases?  I looked for discussion on the
> mailing list around the time your changes were introduced.  I only found
> a message <http://article.gmane.org/gmane.emacs.orgmode/73832> (in a
> thread about how/where #+call lines insert their results) that treats
> the change as a fait accompli, (“I agree that this didn't make all that
> much sense in the past, but with property evaluation and elisp argument
> evaluation now anchored to the point of call [...]”)
> I could have missed something, of course.
> As to the non-scalability, that should be fixed by some combination of
> the parser cache and retrieving all properties at once (via
> ‘org-entry-properties’) rather than ‘org-entry-get’-ing them one-by-one.
> There are a couple recent threads about this.  Here’s one
> <http://mid.gmane.org/address@hidden> about a reimplementation
> of the property API functions in terms of the parser.  Here
> <http://mid.gmane.org/address@hidden>
> the speed tradeoffs of the two approaches are discussed.  (IOW, as
> presently implemented the classical method is not scalable, but said
> unscalability is by no means “inherent”.)
>>> Certainly I agree that the suggested replacement is less capable.
>> Do you have an example of something that it cannot do (modulo the bugs
>> and corners of the deprecated syntax)?
> See the attached file for two examples, one related to #+call lines and
> one not.
> Again, can you say more about what you mean by the bugs and corners of
> the deprecated syntax?  The #+call behavior doesn’t seem like a bug, but
> basically a difference in whether header args are dynamically (wrt point
> of call) or lexically (wrt point of definition) scoped.  Dynamic
> vs. lexical scoping is not a bug, but a matter of taste/language
> design/etc.  Most computer languages with which I’m familiar (Python, R,
> C, Scheme/Lisp, ...) use lexical scoping by default, and elisp has been
> slowly but steadily moving in that direction for years.  Thus this new
> suggested dynamic-type behavior for header args is surprising to me.
> The first demonstration in the attachment (not related to #+calls)
> seems like a much clearer case of deficiency of the new system: an
> inability to inherit different args from different levels.  (Please
> factor away from the nonsense strings in place of “yes” and “no” – I
> wanted to make it clear where each value was coming from, and assure
> that they were not being generated by default.  Of course in a real use
> case the values for these header args would be “yes” and “no”.  Also,
> one could also demonstrate the problem with header args that can take
> an arbitrary string value by design, like :session.)

Initially I thought, to use :header-args+ instead of :header-args would
work, but I was wrong (see below).

| *** Subtree
| :header-args+: :cache quux
| :END:
| *PROBLEM*: we don’t get =:comments foo= from parent headline (“The new way”)
| #+begin_src emacs-lisp
| (awe-show-headers :cache :comments)
| #+end_src
| : ((:comments . "")
| :  (:cache . "quux no"))

I guess one problem that the properties in :header-args are evaluated
From left to right, and if one is found, this one is used? In case of
inheritance (and adding a property via :header-args+) appends it, and if
a same one exists before, the older one is used?

> From your other mail:
> 2014ko irailak 8an, Achim Gratz-ek idatzi zuen:
>> Rainer M Krug writes:
>>> Aaron Ecay <address@hidden> writes:
> [...]
>>>> Are you aware that you can set individual header args as properties?
>>>> Something like (at the file level):
>> Are you aware that this doesn't quite do what you think it does, some of
>> the time, when things become more complex than your example?
> Again, can you say more about what you mean here?  As a personal
> anecdote, I have never been surprised by the behavior of “classic”
> header arg properties.
>>> I was using this deprecated behavior and I was *very* happy with it, but
>>> I am trying to adjust to the new syntax.
>>> So how can I use the new syntax?
>> If you maybe had an example of what you're trying to do instead of
>> asking stuff about things you don't want to do?  Otherwise, have a look
>> at
>> <orgmode.git>/testing/examples/ob-header-arg-defaults.org
> I find the content of this file incredibly dense, and the suggestion
> of its use as documentation bordering on a joke.  (Documentation may
> not exist, and that just means an area for improvement has been found.
> But it’s not as though we’re all going to read that file and suddenly
> understand what you mean.)  It looks like it is trying to demonstrate
> inheritance and overriding of :var header args.  I can’t figure out
> why the #+call in “Overwrite” gets go1, but the addition of “var+ to1”
> in “Accumulate” causes this to shift, not to “to1”, but to “ge1”.
> That is a very confusing interaction (to name just one).  It’s also not
> clear to me how it relates to other header args, since vars supplement
> each other, whereas other types of header replace.

I just looked at it - and there are may things going on which are way to
complex to understand the basics of the use of :header-args (or rather
working with property sets (or lists?) in general?) in org/

A still confused

Rainer M. Krug
email: Rainer<at>krugs<dot>de
PGP: 0x0F52F982

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