Facilities to get Haskell's garbage collector to manage the liveness of values allocated on the R heap. By default, R values remain live so long as the current region is extant. The R garbage collector may only free them after the end of the region. Sometimes, this discipline incurs too high of a memory usage and nested regions are not always a solution.

This module enables registering a callback with the GHC garbage collector. In this way, when the GHC garbage collector detects that a value is no longer live, we can notify the R garbage collector of this fact. The R garbage collector is then free to deallocate the memory associated with the value soon after that.

This module hence offers an alternative, more flexible memory management discipline, at a performance cost. In particular, collections of many small, short-lived objects are best managed using regions.