Why don't purely functional languages use reference counting?

Question

In purely functional languages, data is immutable. With reference counting, creating a reference cycle requires changing already created data. It seems like purely functional la

Answer 1

There are a few things, I think.

• There are cycles: "let rec" in many languages does allow "circular" structures to be created. Apart from this, immutability does usually imply no cycles, but this breaks the rule.
• Ref-counts are bad at lists: I don't know that reference-counted collection works well with e.g. long singly-linked-list structures you often find in FP (e.g. slow, need to ensure tail-recursive, ...)
• Other strategies have benefits: As you allude to, other GC strategies are still usually better for memory locality

(Once upon a time I think I maybe really 'knew' this, but now I am trying to remember/speculate, so don't take this as any authority.)