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RE: a little help with basic elisp


From: Drew Adams
Subject: RE: a little help with basic elisp
Date: Thu, 19 Feb 2015 23:52:06 -0800 (PST)

> (defun gas-push-sr-pair ()
>   "I want to add a apair consisting of a the string I prompted for at the
> mini-buffer, and the string yo"
>   (interactive)
>   (let (to-string)
>       (setq to-string (read-from-minibuffer (concat (thing-at-point
>                                                      'symbol)
>                                                     " to: ")))
>       (add-to-list 'gas-sr-stack  '(to-string . "yo"))))
> 
> When I run this, and do (insert (pop gas-sr-stack)), I get the
> following:
>   gas-pop-word: Wrong type argument: char-or-string-p, (to-string . "yo")
> 
> What's tripping me up is it seems that the values stored in the char-or-
> string-p are to-string and "yo".
> I wanted to store the value which is currently in to-string, and "yo".
> 
> Can someone please explain to me what I am doing wrong?  I'd like to
> understand the language better, and of course solve my concrete problem.

(defvar gas-sr-stack () "...")

(defun gas-push-sr-pair ()
  (interactive)
  (let ((to-string (read-from-minibuffer (concat (thing-at-point 'symbol) " to: 
"))))
    (add-to-list 'gas-sr-stack  `(,to-string . "yo"))))

And you want this instead of just (pop (car gas-sr-stack)):

(let ((gas-sr  (pop gas-sr-stack)))
  (insert (car gas-sr) (cdr gas-sr)))

1. Just bind `to-string' directly to the value you want it to have.
   (Not an error; it's just simpler.)
2. You need to evaluate `to-string' for the cons you want to add to the list.
   Instead, you were inserting the constant cons (to-string . "yo") each time.
   So use a comma inside a backtick - or use (cons to-string "yo").
3. The main problem was that you were trying to insert the cons, not its car
   and cdr (which are strings).  Use `C-h f insert' to see info about `insert'.



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