Stefan Monnier <monnier@iro.umontreal.ca> writes:

>>> I don't understand this change.  Can't it cause two CL-structs to be
>>> vconcat'd together, which wouldn't make much sense?
>> The previous version of `seq-concatenate' did not prevent that, since
>> CL-structs are vectors, thus sequences, and the function was using
>> `sequencep' to determine if the seq had to be converted or not.
>
> Indeed, but if we intend to work for new "sequence" types defined via
> CL-struct, that's still a problem.

Yes, it is still a problem.  One solution would be to test if the seq is
a cl-struct with, in which case we could use `seq-into'.  But then that
would only fix the cl-struct case, not any other.

Nico