Re: Symbol's function definition is void: remove-if-not

[Ted Zlatanov <tzz@lifelogs.com>]

On Mon, 04 Oct 2010 16:15:56 +0900 Katsumi Yamaoka <yamaoka@jpl.org> wrote: 

KY> Ted Zlatanov wrote:
KY> [...]
>> Can you use `gnus-remove-if' with the predicate inverted?

KY> It can be used, if the type of a sequence is `list'.

I know, I meant for Julien's case specifically, I think he's just using
lists.  In general our (Gnus) usage is pretty trivial, without using all
the bells and whistles of the CL function.

KY> For a non- list sequence, we can convert it to a list as the
KY> function `coerce' does (see cl-extra.el).  Though the type of a
KY> modified sequence has to be changed again into that of the original
KY> (if needed).  However, it may be hard to make it work for a hash
KY> table.  So is the genuine `remove-if-not'!

>> It looks like `remove-if-not' is used in several places actually:

>> gnus-art.el:         (remove-if-not pred (mailcap-mime-types))
>> gnus-group.el:                          (remove-if-not 'symbolp collection)))
>> gnus-score.el:                                            (remove-if-not

Those three should be able to use `gnus-remove-if' with the predicate
inverted, I think.

>> gnus-sum.el:             (remove-if-not 'gnus-valid-move-group-p gnus-active-hashtb)
>> gnus-sum.el:             prom (remove-if-not 'gnus-valid-move-group-p gnus-active-hashtb)

KY> The use of `remove-if-not' in gnus-sum.el is a wrong approach since
KY> it doesn't necessarily recognize all the group names in
KY> `gnus-active-hashtb'.  That looks like a normal vector of which
KY> the length is 4096, however it can hold more than 4096 group names
KY> and `remove-if-not' cannot access all of them.

So it's potentially a bug.  I am no expert on ELisp data types,
especially between Emacs and XEmacs.  Should we take this to emacs-devel
or does someone know a good solution?

I think it's acceptable to simply provide `gnus-remove-hashtb-keys-if'
rather than try to reimplement CL.  So maybe that's the right way.

Ted