[urbit]

Right. The way I'd put it is: in system software, the iron law is that you don't make the programmer pay for anything she doesn't need to buy.

What you pay (GC) for the privilege of having pointer cycles in your data is grossly disproportionate to the benefit. Yes, there are a lot of things that are O(k) with pointer cycles and O(log n) without them. If what you buy from this optimization is worth the cost of GC, you are doing a lot of these things... a lot.

[pcmoore]

But looking through code there are lots of references to gc, mark and sweep. Even with acyclic data models memory has to be cleared.