Lacking Natural Simplicity

Random musings on books, code, and tabletop games.

Fun with Emacs: eval-after-load*

Ok, suppose you want to evaluate a particular bit of code after emacs loads a particular emacs-lisp file, but you want to pass values of local variables into that code. The function eval-after-load makes you quote the expression and doesn't allow passing values into the expression. How about this?

(require 'cl)
(defmacro* eval-after-load* (file varlist &rest body)
  "Like `eval-after-load', but bind variables according to VARLIST in
the current environment of the `eval-after-load' expression, not the
environment when BODY is evaluated.  This allows easy passing of values
into BODY.
Each element of VARLIST is a symbol (which is bound to the current value
of that symbol) or a list (SYMBOL VALUEFORM) (which binds SYMBOL to the
value of VALUEFORM in the environment of the `eval-after-load' expression."
  `(eval-after-load ,file
     '(let ,(loop for v in varlist
                  collect (if (symbolp v)
                              `(,v ,(eval v))
                            `(,(car v) ,(eval (cadr v))))
                  into new-varlist
                  finally return new-varlist) ,@body)))
(put 'eval-after-load* 'lisp-indent-function
     (1+ (get 'eval-after-load 'lisp-indent-function)))

Here's a contrived example which demonstrates when things happen.

(let ((f (make-temp-file "tkb-madness" nil ".el"))
      (x 1))
          (let ((buf (find-file f)))
            (insert (format "(y-or-n-p \"In the file '%s'! \")" f))
            (kill-buffer buf)))
        (y-or-n-p "This happens before the eval-after-load*")
        (eval-after-load* f
             (y (y-or-n-p "This happens when the eval-after-load* is executed?"))
             (z 2))
          (y-or-n-p (format "x: %d y: %S z: %d" x y z))
          (y-or-n-p "This happends during the delayed expressions"))
        (y-or-n-p "This happens after the eval-after-load* expression")
        (load f))
    (when (file-exists-p f) (delete-file f))))

You should see something like:

Wrote /tmp/tkb-madness88647vuE.el
This happens before the eval-after-load*(y or n)
This happens when the eval-after-load* is executed?(y or n)
This happens after the eval-after-load* expression(y or n)
Loading /tmp/tkb-madness88647vuE.el (source)...
In the file '/tmp/tkb-madness88647vuE.el'! (y or n)
x: 1 y: t z: 2(y or n)
This happends during the delayed expressions(y or n)
Loading /tmp/tkb-madness88647vuE.el (source)...done

(y-or-n-p is used instead of message so you see each message when it happens.)

Does the eval-after-load* macro make sense?

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