Hello, and thanks for the good work.

This is a design proposal

Both find and canonicalize, as defined, are abstraction breaking, because the data structure is not in a sound state if you don't call rebuild previously. My proposal, in keeping with the spirit of Haskell of correctness first is that:

• the functions named find and canonicalize should call rebuild before querying the data structure (note: in the case where the data structure is already rebuilt, then the work list is empty, therefore rebuild will be very fast anyway)
• for the sake of performance tuning, direct queries to the data structure, called unsafeFind and unsafeCanonicalize would be introduced. With the documentation explaining that the onus is on the programmer to only call them on a “rebuilt” E-graph.