[Refactor] Use expand-file-name instead of concat where possible

configuration.org

@@ -568,8 +568,7 @@ name."
 (defun gpolonkai/visit-org-index ()
   "Visit the root of Org-mode notes."
   (interactive)
-  (find-file-other-window (concat (file-name-as-directory org-directory)
-                                  "index.org")))
+  (find-file-other-window (expand-file-name "index.org" org-directory)))
 #+END_SRC
 
 ** Frame manipulation
@@ -1177,7 +1176,7 @@ Because I’m a sysadmin, too.
   :ensure nil
   :config
   (run-at-time nil (* 5 60) 'recentf-save-list)
-  (add-to-list 'recentf-exclude (concat user-emacs-directory "elpa")))
+  (add-to-list 'recentf-exclude (expand-file-name "elpa" user-emacs-directory)))
 #+END_SRC
 
 ** ~files~
@@ -1355,7 +1354,7 @@ The cookies are from the Hungarian version an ancient MS-DOS based program calle
 (use-package cookie1
   :demand t
   :config
-  (setq cookie-file (concat user-emacs-directory "fortune-cookies.txt"))
+  (setq cookie-file (expand-file-name "fortune-cookies.txt" user-emacs-directory))
   :bind
   (:map gpolonkai/pers-map
    ("k" . cookie)))
@@ -2665,11 +2664,11 @@ This is a big one; I use a lot of customisation here.
   ;; Set up capture templates for blog posts and GT2 related notes
   (add-to-list 'org-capture-templates
                '("p" "Blog post" entry
-                 (file+olp+datetree (lambda () (concat org-directory "blog.org")))
+                 (file+olp+datetree (lambda () (expand-file-name "blog.org" org-directory)))
                  "* %^{Title}  :blog:\n:PROPERTIES:\n:CREATED:  %T\n:END:\n\n%i%?"))
   (add-to-list 'org-capture-templates
                '("g" "GT2 note" entry
-                 (file+headline (lambda () (concat org-directory "gt2-notes.org")) "Captures")
+                 (file+headline (lambda () (expand-file-name "gt2-notes.org" org-directory)) "Captures")
                  "** %^{Title}\n:PROPERTIES:\n:CREATED: %T\n:END:\n\n%a\n\n%i%?"))
   (add-to-list 'org-capture-templates
                '("c" "Item to current Clocked Task" item
@@ -2725,15 +2724,9 @@ This is a big one; I use a lot of customisation here.
   :after
   org
   :config
-  (setq org-ref-bibliography-notes (concat user-documents-directory
-                                           (convert-standard-filename
-                                            "/orgmode/bibliography-notes"))
-        org-ref-default-bibliography '((concat user-documents-directory
-                                               (convert-standard-filename
-                                                "/orgmode/references.bib")))
-        org-ref-pdf-directory (concat user-documents-directory
-                                      (convert-standard-filename
-                                       "/orgmode/bibtex-pdfs"))))
+  (setq org-ref-bibliography-notes (expand-file-name "bibliography-notes" org-directory)
+        org-ref-default-bibliography '((expadn-file-name "references.bib" org-directory))
+        org-ref-pdf-directory (expand-file-name "bibtex-pdfs" org-directory)))
 #+END_SRC
 
 And set up a function to open PDF files with the system pdf viewer, using ~xdg-open~.
@@ -3073,15 +3066,11 @@ See previous versions of the current file.
   :after
   org
   :config
-  (setq bibtex-completion-bibliography (concat user-documents-directory
-                                               (convert-standard-filename
-                                                "/orgmode/references.bib"))
-        bibtex-completion-library-path (concat user-documents-directory
-                                               (convert-standard-filename
-                                                "/orgmode/bibtex-pdfs"))
-        bibtex-completion-notes-path (concat user-documents-directory
-                                             (convert-standard-filename
-                                              "/orgmode/bibliography/helm-bibtex-notes"))
+  (setq bibtex-completion-bibliography (expand-file-name "references.bib" org-directory)
+        bibtex-completion-library-path (expand-file-name "bibtex-pdfs" org-directory)
+        bibtex-completion-notes-path (expand-file-name
+                                      (convert-standard-filename "bibliography/helm-bibtex-notes")
+                                      org-directory)
         bibtex-completion-pdf-open-function 'org-open-file))
 #+END_SRC
 
@@ -3208,7 +3197,7 @@ directory.  It is available from [[http://plantuml.com/download][here]].
          ;; Make sure we have a download location even if XDG is not working
          (cond
           ((xdg-user-dir "DOWNLOAD")
-           (concat (xdg-user-dir "DOWNLOAD") "/plantuml.jar"))
+           (expand-file-name "plantuml.jar" (xdg-user-dir "DOWNLOAD")))
           (t
            "~/Downloads/plantuml.jar"))))
   (defvaralias 'org-plantuml-jar-path 'plantuml-jar-path)