Re: inverse of add-to-list: remove-from-list

[Andreas Schwab <schwab@linux-m68k.org>]

On Okt 13 2020, Boruch Baum wrote:

>> On Okt 13 2020, Uwe Brauer wrote:
>> > But there is, as far as I know, no inverse functionality
>
> 1] Similar to what Andreas suggested, try this:
>
>      (let ((aa '(1 2 3 1 4 1 2)))
>        (delete 2 aa)
>        aa)
>
>    And note that the fine distinction made in the docstring for the
>    `delete' function:
>
>      "If SEQ is not a list, deletion is never performed destructively;
>       instead this function creates and returns a new vector or string.
>
>       Write ‘(setq foo (delete element foo))’ to be sure of correctly
>       changing the value of a sequence ‘foo’.
>
>    So, in the case of SEQ being a list, there is no need to `setq foo'.

This is not true.  If the element to delete is the first element of the
list, it returns the cdr of the list.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
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