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Comment by el_pollo_diablo | Hacker News Reader

Not to mention that they insist on calling every entry of the list a "list head", which makes no sense (hysterical raisins, maybe?). The structure is made of a uniform loop of entries, one of which is used as the actual head & tail, or entry point into the structure.

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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.

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".

Yes, it's terrible, and the fact that their list_add takes parameters backwards from what one might expect, with no types to catch mistakes!

See https://github.com/rustyrussell/ccan/blob/master/ccan/list/_...

Absolutely. Wrapping the distinguished entry point in a new structure type equipped with a thin type-safe wrapper API that covers the most common use case is the way to go.

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