Org-cite (oc-csl) tip: Filtering bibliography for language

[Christian Moe <mail@christianmoe.com>]

Hi,

A tip some of you might find useful:

I wanted to separate sub-bibliographies by language, which is not one of
the out-of-the-box available properties of the PRINT_BIBLIOGRAPHY
keyword.[fn:1] Specifically, I wanted to filter out Norwegian items into
one subbibliography and non-Norwegian ones into another in the same
document.[fn:2]

I found out how to do it with the `PRINT_BIBLIOGRAPHY: :filter
<predicate>' property, which turns out to be used in the function
citeproc-sb--match-p, where it is applied to a var-value list.

I defined a predicate for Norwegian, bibitem-norwegian-p, that matches a
regexp for various labels for Norwegian[fn:3] against the language
value.

#+begin_src elisp
  (defun bibitem-norwegian-p (vv)
    "Returns non-nil (0) if a bibliography item is in
  Norwegian. For use in an org-cite PRINT_BIBLIOGRAPHY filter."
    (let ((itemlang (alist-get 'language vv)))
      (and itemlang (string-match "n[obn][r-bo]?" itemlang))))
#+end_src

Then I could successfully use it as follows:

#+PRINT_BIBLIOGRAPHY: :filter bibitem-norwegian-p

For the list of non-Norwegian items I just needed to define a complementary
function:

#+begin_src elisp
  (defun bibitem-not-norwegian-p (vv)
    (not (bibitem-norwegian-p vv)))
#+begin_src elisp

#+PRINT_BIBLIOGRAPHY: :filter bibitem-not-norwegian-p

Adapt as needed for other languages and use cases.

Refinements welcome. I'm especially wondering what would be an elegant
way to generalize this for more languages without defining a predicate
for each language (given that we cannot pass the language as an
additional argument in the print_bibliography line).

* Footnotes

[fn:1] [[info:org#Bibliography options in the ``biblatex'' and ``csl''
export processors]]

[fn:2] For this to work at all, of course, your CSL JSON or BibTeX has
to contain language information on the items; it should, or English
formatting such as title-casing might be applied inappropriately to
non-English items by some styles.

[fn:3] The regexp is complicated because Norwegian is complicated, my
labeling is inconsistent and I want to match at least no, nb, nn, no-NO,
nb-NO, nn-NO, nor, nob, nno, norsk and Norwegian ...



Yours,
Christian