[antonvs]

In general, there is no “actual” head and tail - you could have multiple references to different parts of the list, and each of them would have a different head. If you’re recursing through a list, at some point every node will be used as the head. This is a common pattern in recursive data structures, particularly in functional languages.

Disclaimer: I haven’t looked at this author’s code, just pointing out that list nodes that consist of (head, tail) are a common pattern with a clear rationale.

[el_pollo_diablo]

Head and tail make sense for persistent lists in functional languages with value semantics, yes.

The intrusive, mutable, doubly-linked loops with reference semantics under discussion are quite different. Although all entries behave identically in the structure itself, one of them is _used_ differently, as a standalone anchor point, while the others are embedded in the list's "elements".