On: Carp – A statically typed Lisp, without a GC, for ...

[pjc50]

That's a question for the underlying allocator, surely?

(Quite often the answer is "it isn't")

[andi999 → pjc50]

Not just for the allocator. I always thought a main point of a garbage collector was heap compactification (shuffling things around so there is more space), but maybe I am wrong.

[cmrdporcupine → andi999]

Nah, only copying / generational collectors do heap compactification. A simple Mark&Sweep collector doesn't, for example. Nor does reference counting. Both of which are used by many Lisp or Lisp-like languages.

Nothing can substitute for a really good allocator.

[andi999 → cmrdporcupine]

So what happens to long running lisp programs? Running out of memory due to fragmentation eventually?

[xxs → andi999]

One would expect at least a provision for a stop the world phase. where all mutator threads get to wait for a massive defragmentation.

[xxs → andi999]

Not every GC has compaction phase though, but generational ones do by design.