Passing parameter to a function in init-file

Question

I'm trying to create a .emacs file that works on multiple platforms. Therefore, I declare a variable with a path for each platform

(defvar macosx-p (string-match "darwin" (symbol-name system-type)))
(defvar gnulinux-p (string-match "linux" (symbol-name system-type)))
(defvar mswindows-p (string-match "windows" (symbol-name system-type)))

(defconst macosx-ps "/Users/xxx/")
(defconst gnulinux-ps "/home/xxx")
(defconst mswindows-ps "D:/xxx")

How can I pass one of the -ps variables to a function like this?

(if macosx-p
   (progn
    (setq org-capture-templates
     '(("t" "TODO" entry (file+headline (concat macosx-ps "file.org") "Inbox")
          "* TODO %?")))))

(if gnulinux-p
  (progn
   (setq org-agenda-files (quote
   ((concat gnulinux-ps "file.org")
    (concat gnulinux-ps "others/"))))))

I want macosx-ps to output my path string.

Answer 1

Instead of defining multiple versions and picking up the right one each time, it would make more sense to define a single variable according to the system that Emacs is running on.

(defconst somepath (cl-case system-type
                     ((gnu/linux gnu gnu/kfreebsd) "/home/xxx")
                     ((darwin) "/Users/xxx")
                     ((windows-nt cygwin) "D:/xxx")
                     (t (expand-file-name "~"))))

Note that if you want to refer to your home directory, you should call expand-file-name rather than hard-code values.

If somepath refers to a directory, call expand-file-name to build a path to a file in that directory. To evaluate part of an expression which is otherwise given in literal syntax, use a backquote rather than a quote, and a comma to indicate subexpressions to evaluate.

(setq org-capture-templates
     `(("t" "TODO" entry (file+headline ,(expand-file-name "file.org" somepath) "Inbox")
          "* TODO %?")))))

Answer 2

As xuchunyang pointed out, I need to add a backquote (´) and , to my list, like this:

(if gnulinux-p
  (progn
   `(setq org-agenda-files (quote
   (,(expand-file-name "file.org" gnulinux-ps)
    ,(expand-file-name "others/" gnulinux-ps))))))

Now everything works.