Lambda the Ultimate

In One Pass Real-Time Generational Mark-Sweep Garbage Collection Joe Armstrong and Robert Virding talk about a very simple garbage collector used in Erlang*.

Traditional mark-sweep garbage collection algorithms do not allow reclamation of data until the mark phase of the algorithm has terminated. For the class of languages in which destructive operations are not allowed we can arrange that all pointers in the heap always point backwards towards "older" data. In this paper we present a simple scheme for reclaiming data for such language classes with a single pass mark-sweep collector.

We also show how the simple scheme can be modified so that the collection can be done in an incremental manner (making it suitable for real-time collection). Following this we show how the collector can be modified for generational garbage collection, and finally how the scheme can be used for a language with concurrent processes.

Unfortunately it's very restrictive. In particular even the "hidden" destructive updates used in a call-by-need language are problematic for this kind of collector.

* I'm not sure whether the described collector is still used in Erlang.