Re: [feature request] The :pre header argument

[Rodrigo Morales <moralesrodrigo1100@gmail.com>]

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I've provided more relevant information on this feature request [[
https://codeberg.org/rdrg109/gists/src/branch/main/feature-request-pre-header-argument.org][here]].
Please consider reading that instead of the first message on this thread.

On Fri, 19 Feb 2021 at 08:33, Rodrigo Morales <moralesrodrigo1100@gmail.com>
wrote:

> You can read this message with proper formatting here (
> https://codeberg.org/rdrg109/gists/src/branch/main/the-pre-header-argument.org
> ).
>
> On Thu, 18 Feb 2021 at 16:52, Rodrigo Morales <
> moralesrodrigo1100@gmail.com> wrote:
>
>>
>> This message contains my thoughts on a feature request which I think
>> would be useful: The =:pre= header argument, it would be used to
>> execute a code block before the code block at point is executed. It
>> would be similar to the behavior of the =:post= header argument.
>>
>> Here's a simple example that shows how =:pre= could be used
>>
>> #+NAME: clean-path-experiments
>> #+begin_src dash
>> if [ ! -z "$my__experiments" ] && [ -d "$my__experiments" ]; then
>>   find ~/e -mindepth 1 -maxdepth 1 -exec rm -rf {} +
>> fi
>> #+end_src
>>
>> #+NAME: tree-command
>> #+begin_src dash
>> tree -a --noreport
>> #+end_src
>>
>> #+NAME: create-dir-for-minimal-reproducible-example
>> #+HEADER: :pre clean-path-experiments()
>> #+HEADER: :post tree-command()
>> #+begin_src python
>> import os
>>
>> [os.makedirs(_) for _ in ["a/foo", "a/bar", "b"]]
>> [os.mknod(_) for _ in ["a/1.txt", "a/2.txt", "a/foo/b.txt",
>> "a/bar/b.txt", "b/b.txt"]]
>> #+end_src
>>
>> #+RESULTS: create-dir-for-minimal-reproducible-example
>> #+begin_example
>> .
>> ├── a
>> │   ├── 1.txt
>> │   ├── 2.txt
>> │   ├── bar
>> │   │   └── b.txt
>> │   └── foo
>> │       └── b.txt
>> └── b
>>     └── b.txt
>> #+end_example
>>
>> I think that such header argument would be useful because of two
>> main reasons:
>>
>> * It would improve readability of code blocks by explicitly expressing
>> dependency
>>
>> By having a header argument for the sole purpose of expressing
>> dependencies between code blocks, the readability of header arguments
>> would be improved. Recall that it is currently possible to express
>> such dependency by calling a code block through a =:var <<name>>=
>> header argument but I think that =:var= header argument must only be
>> used for defining variables (be it from results obtained from
>> different code blocks or literals).
>>
>> The first code block shown below show the differences between using
>> =:var= and =:pre= for the same scenario. =first-code-block= uses the
>> =:var= header argument while the =second-code-block= uses the =:pre=
>> header argument.
>>
>> #+NAME: first-code-block
>> #+begin_src org
>> For our experimentation, let's start with an empty directory and let's
>> execute the first step.
>>
>> ,#+NAME: first-step
>> ,#+HEADER: :results silent
>> ,#+HEADER: :var e=clean-path-experiments
>> ,#+begin_src dash
>> touch first-step.txt
>> ,#+end_src
>>
>> We know execute the second step.
>>
>> ,#+NAME: second-step
>> ,#+HEADER: :results silent
>> ,#+HEADER: :var e=first-step
>> ,#+begin_src dash
>> touch second-step.txt
>> ,#+end_src
>>
>> Finally, we execute the third step.
>>
>> ,#+NAME: third-step
>> ,#+HEADER: :results silent
>> ,#+HEADER: :var e=second-step
>> ,#+begin_src dash
>> touch third-step.txt
>> ,#+end_src
>> #+end_src
>>
>> #+NAME: second-code-block
>> #+begin_src org
>> For our experimentation, let's start with an empty directory and let's
>> execute the first step.
>>
>> ,#+NAME: first-step
>> ,#+HEADER: :results silent
>> ,#+HEADER: :pre clean-path-experiments()
>> ,#+begin_src dash
>> touch first-step.txt
>> ,#+end_src
>>
>> We know execute the second step.
>>
>> ,#+NAME: second-step
>> ,#+HEADER: :results silent
>> ,#+HEADER: :pre first-step()
>> ,#+begin_src dash
>> touch second-step.txt
>> ,#+end_src
>>
>> Finally, we execute the third step.
>>
>> ,#+NAME: third-step
>> ,#+HEADER: :results silent
>> ,#+HEADER: :pre second-step()
>> ,#+begin_src dash
>> touch third-step.txt
>> ,#+end_src
>> #+end_src
>>
>> In my opinion, the second code block looks more readable than the
>> first one.
>>
>> * it would add importance to the =:post= header argument
>>
>> The =:post= header argument can be used in Org Mode 9.3 to execute a
>> given code block after the code block at point is executed; having a
>> header argument that does the opposite of the =:post= header argument
>> would give relevance to the =:post= header argument.
>>
>> --
>> Greetings,
>> Rodrigo Morales.
>>
>> IRC: rdrg109 (freenode)
>>
>

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