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Re: [O] Literate Programming - Continue a Source Block?

From: Eric Schulte
Subject: Re: [O] Literate Programming - Continue a Source Block?
Date: Wed, 08 Jun 2011 13:40:16 -0600
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

> The above is somewhat artificial, but in a proper programming project
> something like this will occur frequently: A new feature will be added
> at some later point and I'll want to update various blocks of code.

Currently the best method is that suggested previously/below of using
named references in the target code block, as suggested below.  While it
shouldn't be overly difficult to add the behavior your described with
something like a ":noweb-append" header argument, e.g.,

  #+begin_src emacs-lisp :noweb-append visual-config

This behavior is not currently implemented.

>> Second solution: create one sole block that will be tangled, and which
>> contains your other blocks (using the <<ref>> syntax), in the order you want.
> I had thought of this, but I find it somewhat lacking. Consider my
> example above. I could have created a <<visual-python>> in my
> <<visual-config>> block. However:
> 1. That requires me to know I'm going to need it later when I write
>    visual-config. 

nit picking here, but while this does require a small edit to
<<visual-config>>, there is no need for prior knowledge of the need for

> 2. If I didn't know I'd need it, I'd have to continually modify various
> parts of the org document every time I add a new feature to my code. I
> find this suboptimal and error prone.

Technically only one edit per new block introduced, which does not seem
overly onerous.

> 3. For me, one of the main motivations to do LP is to document the
> evolution of the project, such that someone else can read the document
> and understand. Part of this is that I want all aspects of a single
> feature to appear under a single heading. When the reader reads the
> document, he shouldn't have to see too many aspects of the code early on
> that will be explained much later in the document.

I agree, this is a motivating example.

> Now the original noweb allows what I'm asking for. If you begin a
> source block with a name of an existing block but append an "="
> symbol, it knows to append to that source block.
> It would be great if org-mode could add that capability.

I agree, and the functionality you describe shouldn't be overly
difficult to implement.

I like the concision of the "=original-name" syntax used by noweb, but I
would lean towards the use of a ":noweb-append" type header argument as
suggested above because currently the names of blocks in Babel carry no
semantic content and I'd prefer to leave it this way.

> Another approach is that if multiple source blocks with the same name
> are found, the default behavior is to concatenate all those source
> blocks together (and then add a header option for overwrite if the
> user wanted to overwrite instead of append).
> Thoughts?

Thanks for the motivating example and the thorough explanation of

I'll certainly put this on my long-term development queue, however, that
does not guarantee an implementation in the near future.  If anyone is
interested in this functionality and is up for writing some elisp I am
happy to offer advice and code pointers immediately.

Best -- Eric

Eric Schulte

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