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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, 15 Jun 2011 21:54:20 -0700
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.50 (gnu/linux)

Achim Gratz <address@hidden> writes:

> Eric Schulte <address@hidden> writes:
>> Does anyone on this list know the noweb system well enough to specify
>> its behavior in this regard, and to describe what functional changes
>> would be required to bring Babel into line with noweb behavior?
> Far from knowing it well, but the basics are, well basic:
> Documentation text is started via '@', code chunks are defined via
> '<<chunk_name>>=' and a given chunk can be extended by '<<chunk_name>>='
> with the same name again, which allows to intermingle documentation and
> definition in a linear fashion.  Code chunk references are just
> '<<chunk_name>>' without the equal sign and can be used non-linearly.
> For comparison with Babel the noweb Hackers Guide is probably a good
> source since it describes the pipeline representation which is used by
> the tools (and should maybe be emulated by the Babel backend).
> http://www.cs.tufts.edu/~nr/noweb/guide.html

Hi Achim,

Thanks for sending along this reference.  That combined with the related
"Literate Programming Simplified" [1] serve as a very interesting
introduction to Noweb.  I have not studied noweb previously and I am
impressed by the simplicity of the pipelined filter-based design.

Noweb and Babel are certainly very different beasts.  Noweb achieves
sparse simplicity allowing use with a variety of tools while Babel lives
inside the very rich environment of Org-mode documents.  Noweb enables
literate programming LP while babel is a reproducible research tool
which also provides support for LP.

It seems that lifting a solution whole-piece from noweb will not make
sense, as noweb does not have a need for unique code block names in the
same way as babel.

How about the following solution, which is based on a new :noweb-ref
header argument.

When expanding ``noweb'' style references the bodies of all code block
with /either/ a block name matching the reference name /or/ a :noweb-ref
header argument matching the reference name will be concatenated
together to form the replacement text.

By setting this header argument at the sub-tree or file level, simple
code block concatenation may be achieved.  For example, when tangling
the following Org-mode file, the bodies of code blocks will be
concatenated into the resulting pure code file.

#+begin_src sh :tangle yes :noweb yes :shebang #!/bin/sh

* the mount point of the fullest disk
  :noweb-ref: fullest-disk

** query all mounted disks
#+begin_src sh
  df \

** strip the header row
#+begin_src sh
  |sed '1d' \

** sort by the percent full
#+begin_src sh
  |awk '{print $5 " " $6}'|sort -n |tail -1 \

** extract the mount point
#+begin_src sh
  |awk '{print $2}'
This should provide feature-parity with noweb, and satisfy most LP needs.

Best -- Eric

[1]  www.cs.tufts.edu/~nr/pubs/lpsimp.pdf

Eric Schulte

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