[Jtsummers]

I wrote that quickly and should have edited it for clarity. What I meant was a new collection type that could be treated as a sequence.

https://www.lispworks.com/documentation/HyperSpec/Body/17_a....

None of the functions operating on sequences are generic, so you cannot create your own type and do a `defmethod` and have them automatically adapt to it. And unlike `print-object` which gets used by format and print and others, there's also no "protocol" (or whatever term you like) generic function you can implement which will make your collection acceptable as a sequence.

You could build something like this, and maybe shadow the standard functions so that it's not a new set of functions from a user perspective, but it's a notable absence in a language with a rich OO system through CLOS. It makes sense that it wasn't in the original spec, but I still think it would have been something that would have been added if the development of CL (as a standard) had continued.

[Pay08]

Oh, I understand. For what it's worth, some implementations do have that as an extension, although I've personally never used it. See http://www.sbcl.org/manual/#Extensible-Sequences.