1. Shouldn't the last line be (watch file-name delegate) so that it continues to watch after the first update? Or should that be optional?
2. It might be a good idea to pass file-name to the delegate. Not strictly necessary, and doesn't give any benefit in this example, but it could mean that you sometimes don't need to use a fn as the delegate. If you didn't want to pr "reloaded" for instance, you could just do (watch file-name load).
3. Is the hash table really necessary? Here is a version without it:
Ah, so loading the file makes it watch itself. You need to do the load in a thread then?
I still fail to see how the hash table helps since my version above should do exactly the same as yours. I would see the point if you made a thread check all files in the table, and made the first call to watch launch the thread, while subsequent calls just add entries to the table.