Alternatives to long complex format statements in emacs-lisp

Posted January 20, 2014 at 09:50 AM | categories: emacs-lisp | tags:

At one point I had a string I wanted to fill in with a bunch of variables. 

(insert (format"
 :PROPERTIES:
  :Custom_ID: %s
  :AUTHOR: %s
  :JOURNAL: %s
  :YEAR: %s
  :VOLUME: %s
  :PAGES: %s
  :DOI: %s
  :URL: %s
 :END:
[[cite:%s]] [[file:%s/%s.pdf][pdf]]\n\n"
key author journal year volume pages doi url key jorg-bib-pdf-directory key ))

I find that very difficult to use, because it is tedious to make sure all the variables are in the right order, and it is difficult to change later. In Python, you would be able to put named expansions in, e.g. {author} and then used named arguments. That does not exist as far as I know in emacs-lisp.

Below is an alternatme approach that uses concat to construct this string. 

(let ((key "kitchin-2014")
      (author "Kitchin, J. R.")
      (journal "HACS")
      (year "2014")
      (volume "1")
      (pages "1--10")
      (doi "10.1.1.109/hacs.1.10")
      (url "http://hacs.org/10.1.1.109/hacs.1.10")
      (jorg-bib-pdf-directory "/home/jkitchin/pdfs"))

(concat "
 :PROPERTIES:
  :Custom_ID: " key "
  :AUTHOR: " author "
  :JOURNAL: " journal "
  :YEAR: " year "
  :VOLUME: " volume "
  :PAGES: " pages "
  :DOI: " doi "
  :URL: " url "
 :END:
[[cite:" key "]] [[file:" jorg-bib-pdf-directory "/" key ".pdf][pdf]]\n\n"))

 :PROPERTIES:
  :Custom_ID: kitchin-2014
  :AUTHOR: Kitchin, J. R.
  :JOURNAL: HACS
  :YEAR: 2014
  :VOLUME: 1
  :PAGES: 1--10
  :DOI: 10.1.1.109/hacs.1.10
  :URL: http://hacs.org/10.1.1.109/hacs.1.10
 :END:
[[cite:kitchin-2014]] [[file:/home/jkitchin/pdfs/kitchin-2014.pdf][pdf]]

That is kind of interesting. It is a little tedious to use all the quotes. It seems like there should be soemthing like named expansions. Let us write one of our own. We will use a regular expression to find {:keyword} and a plist. There is a regexp to match this, and then we can take the characters from position 1 to the second to last character as the keyword. That is not beautiful to me, but it works here. Then we just get the keyword from the plist. The keywords in a plist are symbols, and we will have strings. We have to use the intern function to convert them to symbols. 

(defun expand-template (s plist)
  "expand a template containing {:keyword} with the definitions in plist"
  (replace-regexp-in-string "{\\(:[^}]+\\)}" 
                            (lambda (arg) 
                              (let ((keyword (intern (substring arg 1 -1))))
                                (format "%s" (plist-get plist keyword)))) s))

(let ((template "
 :PROPERTIES:
  :Custom_ID: {:key}
  :AUTHOR: {:author}
  :JOURNAL: {:journal}
  :YEAR: {:year}
  :VOLUME: {:volume}
  :PAGES: {:pages}
  :DOI: {:doi}
  :URL: {:url}
 :END:
[[cite:{:key}]] [[file:{:pdf-dir}/{:key}.pdf][pdf]]\n\n"))

(expand-template template
                 '(:key "kitchin-2014"
                        :author "Kitchin, J. R."
                        :journal "HACS"
                        :year 2014
                        :volume 1
                        :pages "1--10"
                        :doi "10.1.1.109/hacs.1.10"
                        :url "http://hacs.org/10.1.1.109/hacs.1.10"
                        :pdf-dir "/home/jkitchin/pdfs")))

 :PROPERTIES:
  :Custom_ID: kitchin-2014
  :AUTHOR: Kitchin, J. R.
  :JOURNAL: HACS
  :YEAR: 2014
  :VOLUME: 1
  :PAGES: 1--10
  :DOI: 10.1.1.109/hacs.1.10
  :URL: http://hacs.org/10.1.1.109/hacs.1.10
 :END:
[[cite:kitchin-2014]] [[file:/home/jkitchin/pdfs/kitchin-2014.pdf][pdf]]

That is pretty close to what I am used to from python! I am surprised there aren't other solutions for this around. I looked, and couldn't find them.

Copyright (C) 2014 by John Kitchin. See the License for information about copying.

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