Echo Area


3 October 2012 2:35 AM (scheme | xdg | coding)

Since I have nothing better to say and still want to say something, here is some nonsense:

I've been having an issue with loading configuration and data files. The problem is that I like the XDG Base Directory Specification and am trying to write my software in such a way that it supports both this and the usual(/old) folder in $HOME approach.

This doesn't sound all that difficult, nor is it, but still I was making a lot of mistakes with it, because I don't just want to support something, I don't want to force whomever (nobody but me, really) uses my software to be forced in to anything. So first I need to check if the XDG environment variables exist, if they do then I have to see if the file I want to load exists in that directory, if it doesn't and one does exist in $HOME I want that one, but if the one in home doesn't exist either, I want the one in the XDG folder again. It gets messy.

I feel that I may have it now, though…

(define (stored-file xdg-env file)
  "Try to get FILE stored either in XDG-ENV or the home directory."
  (let ((xdg (getenv xdg-env))
        (stored-file (string-append
                      (getenv "HOME") "/.project/" file)))
    (unless (or (file-exists? stored-file) (not xdg))
      (set! stored-file (string-append xdg "/project/" file)))

(define (config-file file)
  (stored-file "XDG_CONFIG_HOME"))

(define (data-file file)
  (stored-file "XDG_DATA_HOME"))

(define (rc-file)
  (config-file "rc.scm"))

(define (list-file)
  (data-file "list.scm"))

The stored-file function first assumes that we will want to grab it from the directory in $HOME, when it can't verify that that particular file exists and knows that the XDG variable isn't empty it will instead return a reference to the file in that directory.

All the other functions are just there to make it clear and convenient to load these files and not specifically necessary. The good part of this function, in my opinion, is that is separates configuration and data files from each other in code, but will just grab it all from the same directory when working with the $HOME directory. This, of course, can create naming conflicts, but if you have naming conflicts this way you might get confused by what you're doing here or there anyway.

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