Let's consider Revision.of_yojson_exn. Merlin reports its type as Revision.t of_yojson_exn. All of this occurs in the library Legilogic_lib. What's going
on here is that Types.Revision is a DbInt, and that includes
Persisting.PersistableS, which includes Yojsoning.YojsonableS, which
contains a value labeled of_yojson_exn, which is also of type
of_yojson_exn (also defined in Persisting). That type is a function, yojson -> 'a.
Rule 1: NEVER, EVER send any effectful (as opposed to informative) message to anyone else (including the blockchain, but not limited to it), until you've committed the fact that you're sending the message.
Rule 2: EVERY SINGLE effectful message whatsoever MUST be idempotent.