Re: let*: Wrong type argument: stringp, nil

[Hongyi Zhao]

On Sat, Sep 25, 2021 at 10:45 PM Stephen Berman <stephen.berman@gmx.net> wrote:
>
> On Sat, 25 Sep 2021 21:49:38 +0800 Hongyi Zhao <hongyi.zhao@gmail.com> wrote:
>
> [...]
> > But the actual demand exceeds the simple processing above, I mean, the
> > real project maybe located under a specific folder with multiple level
> > subdirectories. In this case, when I open a python file, the function
> > should do the following: Search the current directory and its parent
> > directories at all levels in turn. Once the ".python-version" file is
> > found, activate the corresponding environment and exit the cycle;
> > Otherwise, continue to search upwards until the  certain top level
> > directory, say, $HOME. Based on the above requirements and the code
> > snippets given here [1-2], I finally figured out the following
> > solution:
> >
> > -------
> > (defun parent-directory (dir)
> >   (unless (equal (getenv "HOME") dir)
> >     ;file-truename or directory-file-name
> >     (file-name-directory (directory-file-name dir))))
> >
> >
> > (defun find-file-in-heirarchy (current-dir fname)
> >   "Search for a file named FNAME upwards through the directory
> > hierarchy, starting from CURRENT-DIR"
> >   (let ((file (concat current-dir fname))
> >         (parent (parent-directory (expand-file-name current-dir))))
> >     (if (file-exists-p file)
> >         file
> >       (when parent
> >         (find-file-in-heirarchy parent fname)))))
> >
> >
> > (defun try/pyvenv-workon ()
> >   (when (buffer-file-name)
> >       (let ((file (find-file-in-heirarchy (buffer-file-name)
> > ".python-version")))
> >         (when (file-exists-p file)
> >           (pyvenv-workon (with-temp-buffer
> >                            (insert-file-contents file)
> >                              (nth 0 (split-string
> > (buffer-string)))))))))
> >
> > (add-hook 'python-mode-hook 'try/pyvenv-workon)
> > -------
> >
> > It works like a charm. But any suggestions/enhancements/comments will
> > be greatly appreciated.
> >
> > [1] https://stackoverflow.com/a/14096693  (*)
> > [2] http://sodaware.sdf.org/notes/emacs-lisp-find-file-upwards/
> >
> > * Indicated that this is my main reference source code.
>
> Doesn't using the built-in Emacs function `locate-dominating-file', as
> mentioned in the stackoverflow thread, work just as well as
> `find-file-in-heirarchy'?

According to my current test, it can indeed work very well. But I
don't know if there are edge cases which this solution doesn't treated
correctly. The built-in Emacs function `locate-dominating-file' relies
on several other predefined functions, and It has been tested and
iterated a lot. So, maybe it's more robust.

HZ