It seems that under some circumstances it might be good for a programmer to be able to tell the implementation not to remember something. In particular, intermediate data structures may be remembered for much longer than they should be. If I am not mistaken, full laziness (which I think ghc uses with -O ?) can make this worse. Would it be beneficial to have some kind of annotations to help deal with this? I don't really know how it would be implemented. Take a standard sort of example: fib n = let f = 0:1:zipWith (+) f (tail f) in f !! n -- code that first calculates fib 1000, then fib 3, fib 4, then does some other stuff I believe that the entire list will be maintained (when compiled with ghc -O) after calculating fib 1000, despite the fact that it will never be used again. If I could say instead fib n = let forget f = 0:1:zipWith (+) f (tail f) in f !! n and somehow get it to forget about f as often as possible (somehow suppressing laziness in this case). I would certainly want to forget about it whenever it goes out of scope, but in this case I would really want to somehow ensure that the list is never held entirely in memory (forgetting it as it is built in f !! n).