Re: defining a setter function with gv.el

[Ivan Kanis <ivan.kanis@googlemail.com>]

Hi Stefan,

As I was trying to make sense of it I tried the following in my
*scratch* buffer:

(setq lexical-binding t)

(defun alist-get (key alist)
  "Get the value associated to KEY in ALIST."
  (declare
   (gv-expander
    (lambda (do)
      (macroexp-let2 macroexp-copyable-p k key
        (gv-letplace (getter setter) alist
          (macroexp-let2 nil p `(assoc ,k ,getter)
            (funcall do `(cdr ,p)
                     (lambda (v)
                       `(if ,p (setcdr ,p ,v)
                          ,(funcall setter
                                    `(cons (cons ,k ,v) ,getter))))))))))))


(setq foo '((bar . foo) (baz . qux)))

(alist-get 'bar foo) => "Get the value associated to KEY in ALIST."

It's as if everything in declare was not evaluated. Where did I err?

Stefan Monnier <monnier@IRO.UMontreal.CA> wrote:

> and the code we want to generate for a `setf' is along the lines of:
>
>         (let* ((k KEY)
>                (a ALIST)
>                (p (assoc k (alist-getter a)))
>                (v VAL))
>           (if p (setcdr p v)
>             (alist-setter a (cons (cons k v) (alist-getter a)))))

Yes this is what needs to be generated. I don't understand why there
are two lambdas in alist-get. There is no map type function so I don't
understand what they do.

Is there any chance you would uncomment this function so that I can use
it in my code?

Take care,
-- 
Ivan Kanis
http://ivan.kanis.fr

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