Re: [ANN] BREAKING CHANGE -- removing #+BABEL file-wide property lines

[Eric Schulte <schulte.eric@gmail.com>]

Darlan Cavalcante Moreira <darcamo@gmail.com> writes:

> It's excellent that now babel understands multiple values in the "var"
> property (I was one of the people that wanted this), but "There Is One More
> Thing".
>
> Would it be feasible to inherit variables from parent sub-trees?
> Effectively, I'd like to append new values in lower level sub-trees, but
> AFAIK setting the var property in a sub-tree will still replace the value
> set in the parent sub-tree.
>

Currently every new property specification entirely replaced previous
specifications with the same name.

>
> That is, in the example below the level-2 sub-trees would not have the foo
> variable passed to babel.
> * Code with foo
>   :PROPERTIES:
>   :var:      foo=1
>   :END:
>
> ** Code only with bar
>    :PROPERTIES:
>    :var:      bar=2
>    :END:
>    src_block
> ** Code only with baz
>    :PROPERTIES:
>    :var:      baz=3
>    :END:
>    src_block
>
> Maybe a special keyword, such as "inherit" (or "append") could be used to
> incorporate variables defined in the parent sub-tree, such that the example
> would become
> * Code with foo
>   :PROPERTIES:
>   :var:      foo=1
>   :END:
>
> ** Code with foo and bar
>    :PROPERTIES:
>    :var:      bar=2, inherit
>    :END:
>    src_block
> ** Code with foo and baz
>    :PROPERTIES:
>    :var:      baz=3, inherit
>    :END:
>    src_block
>
> This should not affect global variables and "inherit" would inherit
> variables defined only in the parent sub-tree (unless it also contains the
> inherit keyword).
>
> As a use case scenario, suppose I need to perform simulations for a few
> different scenarios, each with small variations. This would allow me to
> define common variables for a scenario in a higher level sub-tree and more
> specific variables in the lower level sub-trees.
>

This sounds somewhat similar to my suggestion in reply to Rainer's
email.

Best -- Eric

>
> --
> Darlan Cavalcante
>
>
> At Fri, 21 Oct 2011 22:24:25 +0200,
> Christian Moe <mail@christianmoe.com> wrote:
>> 
>> Hi,
>> 
>> Yes, that works nicely, and should solve Rainer's problem.
>> I haven't been able to think of anything else that can't be handled by 
>> properties.
>> 
>> And I do think it's a good idea to winnow down the syntax a bit, even 
>> if things break. I just like to grumble.
>> :-)
>> 
>> Yours,
>> Christian
>> 
>> On 10/21/11 7:37 PM, Eric Schulte wrote:
>> > Nice idea.  This same issue with "var" arose when we first started
>> > allowing header arguments to be specified inside subtree properties.
>> > I've just implemented your suggestion so the following are now possible.
>> >
>> > #+PROPERTY: var foo=1, bar=2
>> > #+PROPERTY: cache yes
>> >
>> > #+begin_src emacs-lisp
>> >    (+ foo bar)
>> > #+end_src
>> >
>> > #+results[be32e67491d4e92f75769aebe423c20ca01626fe]:
>> > : 3
>> >
>> > and
>> >
>> > #+begin_src emacs-lisp :var foo="this", bar="that"
>> >    (concat foo " " bar)
>> > #+end_src
>> >
>> > #+results[3cde077efa81f1ca24a62ac264dbd5776b6e0054]:
>> > : this that
>> >
>> > Thanks for the suggestion and I hope the above is a sufficient
>> > replacement for the now-missing #+BABEL: syntax.
>> >
>> > Cheers -- Eric
>> 
>> 

-- 
Eric Schulte
http://cs.unm.edu/~eschulte/