Has anyone done any research into fusing operations that involve thawing some data, mutating it, and then freezing it again? Data.Vector does something similar; it turns vectors into streams, operates on the streams, and then turns them back into vectors. It can fuse these operations by removing intermediate However, I've done a bit of preliminary work on a fusion system that works on operations of the form runST $ do x' <- thaw x foo x' freeze x' and yields promising results in some cases. This could be useful for data structures that aren't stream-able, but suffer from lots of unnecessary freezing and unfreezing. This seems like the sort of thing that someone would have already done, so I wanted to check if anyone knew of any previous work on this. Cheers, Will