Insisting on a single linked lists as the fundamental data structure is not necessary, that much I agree, but I would say, if you need del x[5], then in some ca

Insisting on a single linked lists as the fundamental data structure is not necessary, that much I agree, but I would say, if you need del x[5], then in some cases you should not be using a list, but potentially a persistent data structure/PFD. This is an area that Lisps should invest in: Batteries included for good functional data structures.