Hi Joachim,
...
I think one problem with this approach is that now, until "x r'" is evaluated, you keep both r and r' alive. If r was _not_ retained by anything else, then you are now preventing the GC from freeing it and hence increasing the memory footprint.
Good remark, this can be solved with weak pointers, although I don't know how efficient they are. ---------------------- The next version of the proposal Replace every record update r' = r { x = y } with r' = r { x = update (weak r) r' (x r) y) } in generated code if some sharing aware optimization flag is enabled. Auxilary functions: weak :: a -> Weak a -- make a weak pointer which is not followed by GC update :: Weak r -> r -> x -> x update r_old r_new x_old x_new = unsafePerformIO $ do eval x_new b <- x_old === x_new when b (replace r_new r_old) return x_new (===) :: a -> a -> IO Bool -- pointer-equality for boxed values, equality for unboxed values replace :: a -> Weak a -> IO () -- replace thunks in the heap -- do nothing if the weak pointer was gone Cheers, Peter