I don't have any specific info about what the parent post was talking about, but for those that were curious about Haskell's garbage collector in general (like me), here is a Stack Overflow link with some explanation:

http://stackoverflow.com/questions/15236238/current-state-of...

And here is the GHC (Haskell compiler) docs on controlling the garbage collector:

http://www.haskell.org/ghc/docs/7.0.1/html/users_guide/runti...