I have a Haskell program that caches data in a tree. Unfortunately, the tree grows to exceed the available memory over time. In a different language, where I might be handling the caching myself, rather than relying on laziness within the language, I might work round this by keeping track of which leaves in the tree were more recently used, and, when memory run slow, deleting those that have not been used for some time (by the nature of the problem, access to particular caches tend to be grouped, so a long-unused cache can be deleted without much performance penalty). What options do I have in Haskell? I'm interested both in general solutions (maybe some compilers do this anyway?) and in approaches to structuring the program so that I can control caching in more detail. Thanks, Andrew -- http://www.acooke.org/andrew