Re: What's missing in ELisp that makes people want to use cl-lib?

[Michael Heerdegen]

João Távora <joaotavora@gmail.com> writes:

> This is all interesting, until one ponders what happens if an existing
> seq.el user somewhere has:
>
> (cl-defmethod seq-contains-p ((seq my-voodoo-seq)
>                               (elt (eql :secret-voodoo)) &optional _tesfn)
>   (invoke-voodoo-priests seq))
>
> making use of seq.el's support for abstract polymorphic sequences.
>
> With seq.el 2.24 a seq-difference operation would consider this user's
> method, with seq.el 2.24.dmitry (i.e. your fast seq-difference-3) it 
> simply won't.  This user's code is clearly broken.

This is something to keep in mind indeed.  But this problem only appears
when a new generic is added to seq.el.  Then the programmers defining
implementations of the generics needs to update definitions to include a
definition for the new generic - s?he probably wants to do that anyway.

We will surely not have to add a new generic very often.

> But was the user allowed to do that in the first place?  If not,
> why is seq-contains-p a public generic function?

We have lost our way a little more, because cl-lib would support your
my-voodoo-seq not very well.

Michael.