A side question. How can I find what hooks are available? By looking
at the source and finding what functions are defined as refs? (I find
that parse_toplevel_phrase, parse_use_file, and toplevel_startup_hook
are defined as refs in toploop.ml, so they can be replaced?)
That's the idea. Only the refs exposed in the mli can be set from the outside though.
What if there is no such hook? For the type debugger, I want to call
a specific function whenever a type error occurs in the second
execute_phrase (right after "with exn ->") in toploop.ml. But there
is no hook there. Since the execute_phrase function is not defined as
a ref, I cannot replace it, either. What can I do then?
If there is no hook, I'm afraid there is no good solution at the moment; you need to patch the toplevel library, or copy some of its code and modify it.