Load Twin Emacs Code

This function does exactly what ff-find-other-file does, and less. I did not know about ff-find-other-file when I wrote and posted this code. I wish I could delete this page, but PagePruning? seems to say I'm stuck with it. Oh, well. This page can serve as a reminder to look *really* hard in emacs before you implement a new function. Odds are it's already there. -ScottDe

: Ha! I wrote that a version of that function too. I didn't know about ff-find-other-file. BTW, my version of emacs (XEmacs 20.4) doesn't seem to have ff-find-other-file. Is it part of a particular package? -- JimWeirich

Don't worry about it, the same is true for just about any emacs feature. I once wrote a CORBA ORB in emacs lisp, and was shocked to find a few days later that there was already a (much) better one around. -- LukeGorrie

Here is some elisp to switch between twins [.h and .cpp files for the same class]. The entry point is "load-twin". It works if the files are stored in the same directory or if you have parallel "src" and "include" directories for your files.

I am not really a lisp person, hope this code isn't too ugly. If you try it and it doesn't work, let me know, I may have forgotten to include a helper function (I extracted this code from a couple of .el files I wrote, hopefully I got it all). You need to get the AnaphoricLispMacros before this code will work.

-ScottDe

 (defun my-file-exists-p (file-name)
  (if (file-exists-p file-name) file-name nil))

 (defun twin-file-name-helper (cur-file cur-ext twin-ext cur-dir twin-dir)
   (if (string-match (concat ".*" cur-ext) cur-file)
       (aif (my-file-exists-p
             (my-replace-lisp-string cur-ext twin-ext
                                     (my-replace-lisp-string cur-dir twin-dir
                                                             cur-file)))
            it
            (my-file-exists-p (my-replace-lisp-string
                               cur-ext
                               twin-ext cur-file)))))

 (defun twin-file-name (cur-file)
   (cond
    ((twin-file-name-helper cur-file "cpp$" "h" "/src/" "/include/"))
    ((twin-file-name-helper cur-file "inc$" "h" "/src/" "/include/"))
    ((twin-file-name-helper cur-file "h$" "cpp" "/include/" "/src/"))
    ((twin-file-name-helper cur-file "h$" "inc" "/include/" "/src/"))))

 ;; keep find-file-noselect from creating redundent buffers for same file

 (setq find-file-existing-other-name t) 

 (defun load-twin ()
   "Load the twin of the header or implementation file"
   (interactive)
   (let ((file-name (twin-file-name (buffer-file-name))))
     (cond ((not file-name) (ding t))
           ((file-exists-p file-name) 
            (find-file file-name))
           (t (ding t)))))

 ;; you also need the following helper functions

 (defun my-lisp-substring (str from to)
   (let ((last-char (1- (length str))))
     (cond ((<= from last-char) (substring str from to))
       (t nil))))

 (defun my-replace-lisp-string (f-str r-str str)
   (if (string-match f-str str)
       (let ((first-part (my-lisp-substring str 0 (match-beginning 0)))
         (last-part (my-lisp-substring str (match-end 0) nil)))
     (concat first-part r-str last-part))
     str))

CategoryEmacs