How to set a variable name with a variable?

Question

I want to do this.

(let ((myvar "my/variable")
      (myval "Some Value"))
  (setq myvar myval))

The manual method is:

(setq "my/variable" "Some Value")

Here is the full code: As you can see the values are shown in the messages area but they are not set as variables.

(define-error 'my-own-errors   "My Errors")
(define-error 'wrong-arguments "Wrong Arguments" 'my-own-errors)
(define-error 'file-missing    "File Missing"    'my-own-errors)
(define-error 'unknown         "Unknown Error"   'my-own-errors)

(defun my/map--nested-alist (callback NLIST)
  "Call CALLBACK with key value pairs."
  (cond ((stringp NLIST)
         (unless (file-exists-p NLIST)
           (error (signal 'file-missing '(NLIST "was not found.")))))
        ((not (listp NLIST))
         (error (signal 'wrong-arguments '(NLIST "is not a list"))))
        ((listp NLIST) ; Ideally check the list for (dot . notation)
         t)
        (t
         (error (signal 'unknown '(NLIST "was not found.")))))
  (dotimes (x (length NLIST))
    (let* ((group (nth x NLIST))
           (cl (nth 0 (cdr group))) ; cons or list
           (key (car group))
           ;; if list use nth if cons (foo . bar) use cdr
           (val1 (if (consp cl)
                     (car cl)
                   (nth 0 cl)))
           ;; TODO: I could not figure out how to account for cons (dot . notation)
           ;; for now don’t use a '.' in the file, will look at it later.
           (val2 (if (consp cl)
                     (nth 1 cl)
                   (cdr cl))))
      (funcall callback
               `(:key ,key :val1 ,val1 :val2 ,val2)))))

(my/map--nested-alist (lambda (x)
                        (let* ((key   (format "%s" (plist-get x :key)))
                               (myvar (format "%s" (plist-get x :val1))))
                          (progn
                            (message "key is: %s val: %s" key myvar)
                            (setq key myvar))))
                      (with-temp-buffer (insert-file-contents "~/.config/emacs/.data/fakefile")
                                        (read (buffer-string))))

Here is the file in ~/.config/emacs/.data/fakefile

(("my/website"  ("~/Documents/website"  "Website stuff Comment"))
 ("my/journals" ("~/Documents/journals"                     nil))
 ("my/example"  ("~/Documents/example"        "Example Comment")))

Answer 1

intern turns a string into a symbol, then you can use set on that symbol:

(set (intern "var") "some value")
var
⇒ "some value"

or

(setq varname "var")
(set (intern varname) "some value")
var
⇒ "some value"

(setq NAME VALUE) is a contraction of (set 'NAME VALUE) (notice the quote, hence the "q"). setq suppresses the evaluation of its first argument (think about it, most Elisp function would expand NAME to its value as a variable, e.g. (concat var "some string"). In fact, setq isn't a function, it is a special form). You don't need this when you invoke intern, that's why you use set.

Answer 2

The variable needs to be a symbol, not a string: my/variable, not "my/variable".

(let ((myvar 'my/variable)
      (myval "Some Value"))
  (set myvar myval)
  (message "MYVAR: %S" myvar))

Of course, if you want to change a global (i.e., dynamically bound) variable named my/variable then you need to declare it as such:

(defvar my/variable "Some Value")

Or

(defvar my/variable)

(let ((myval "Some Value"))
  (setq my/variable myval))

Or even just this (not inside a let):

(setq my/variable "Some Value")

It all depends on what you want to do. What that is isn't clear.