Elisp newbie string to symbol help

Elisp newbie string to symbol help

[Thomas Ingram]

I'm looking for some help with a simple function I am trying to write. 
I'm a long time Emacs user but I have little experience with Emacs lisp. 
The issue I am having is with the load-theme lines.

(defun my/theme-toggle ()
   "Toggle between light to dark theme."
   (interactive)
   (require 'custom)
   (let* ((current-theme (symbol-name (car custom-enabled-themes)))
      (theme (substring current-theme 0
                (- (length current-theme)
                   ; Probably a better way to do this with regex?
                   (if (string-suffix-p "dark" current-theme)
                   (length "-dark")
                 (length "-light"))))))
   (if (string-suffix-p "dark" current-theme)
       (load-theme (concat theme "-light"))
     (load-theme (concat theme "-dark"))))
   ;; (spaceline-emacs-theme)
   (start-process "toggle Gtk theme" nil "~/bin/change-theme" "toggle"))

I get the message "load-theme: Invalid theme name ‘spacemacs-dark’" 
which doesn't make sense as that is a theme I have installed.  I've 
tried quoting those lines but then it doesn't evaluate. How can I 
properly pass this concatenated string to load-theme?

I vaguely understand that it is expecting a symbol not a string and I've 
tried passing the string to make-symbol but that just changed the error 
to "Undefined Custom theme spacemacs-dark"

Any help is appreciated.

Thanks,

Thomas Ingram

Re: Elisp newbie string to symbol help

[Michael Heerdegen]

Thomas Ingram <taingram@mtu.edu> writes:

> I vaguely understand that it is expecting a symbol not a string and
> I've tried passing the string to make-symbol but that just changed the
> error to "Undefined Custom theme spacemacs-dark"

`make-symbol' returns an uninterned symbol which is different from the
symbol you want (though it has the same name).  You want `intern' or
`intern-soft'.  For the details see the manual.

Michael.

Re: Elisp newbie string to symbol help

[Thomas Ingram]

Thank you, that's exactly what I was looking for!

On 3/7/19 12:08 PM, Michael Heerdegen wrote:
> Thomas Ingram <taingram@mtu.edu> writes:
>
>> I vaguely understand that it is expecting a symbol not a string and
>> I've tried passing the string to make-symbol but that just changed the
>> error to "Undefined Custom theme spacemacs-dark"
> `make-symbol' returns an uninterned symbol which is different from the
> symbol you want (though it has the same name).  You want `intern' or
> `intern-soft'.  For the details see the manual.
>
> Michael.

Re: Elisp newbie string to symbol help

[Stefan Monnier]

>   (if (string-suffix-p "dark" current-theme)
>       (load-theme (concat theme "-light"))
>     (load-theme (concat theme "-dark"))))

Aka

    (load-theme (concat theme (if (string-suffix-p "dark" current-theme)
                                  "-light" "-dark")))

-- Stefan