On Thu, 2 Mar 2017, Nicolas Petton wrote:

> Tino Calancha <tino.calancha@gmail.com> writes:
>
>
>> (cl-loop for i below 3 collect
>>   (let ((map (list (cons 0 3)
>>                    (cons 1 4)
>>                    (cons 2 5))))
>>     (map-delete map i)
>>     (null (map-elt map i))))
>> => (nil t t) ; The first pair, i.e. '(0 . 3) is not permanently deleted.
>
> The alist is indeed modified within the `map-delete' function, but in an
> unexpected way: if the first key is deleted, the variable `map' is
> `setq'ed, which has no effect outside of the function.
>
> One fix would be to make `map-delete' a macro:
>
> (defmacro map-delete (map key)
>  "Delete KEY from MAP and return MAP.
> No error is signaled if KEY is not a key of MAP.  If MAP is an
> array, store nil at the index KEY.
>
>  MAP can be a list, hash-table or array."
>    `(macroexp-let2 nil key
>       (map--dispatch ,map
>         :list (setf (alist-get ,key ,map nil t) nil)
>         :hash-table (remhash ,key ,map)
>         :array (and (>= ,key 0)
>                     (<= ,key (seq-length ,map))
>                     (aset ,map ,key nil)))
>       ,map))
>

After this patch if i run the above recipe i get an error:
let*: Symbol¢s function definition is void: map--dispatch