Hello everybody, I have a little question I wanted to run by the folks here. I've run into it several times over the past few years and would love to lock down a good answer. What's the best way to "fingerprint" a Haskell object into, say, ByteString, so that this fingerprint can be used as the "lookup key" in a database (for example) and be trusted that it will remain constant over time even as the underlying libraries evolve? Here's a simple example: - Say I'm building a manual index on top of a key-value store (redis, dynamodb, etc.) - I want my keys to be arbitrary tuples (or similar records) that may contain various fields in them - I would like to avoid ad-hoc, hand-written MyTuple -> ByteString and ByteString -> MyTuple conversions. However, Generic derivations, template-haskell, etc. are acceptable - Notice how your fingerprint, which is used as a lookup key in the database, has to remain stationary. If it changes even by a single bit over time for the same MyTuple, the key-value store will NOT be able to find the index associated with MyTuple at this later time Here are some ideas (and related concepts) I've considered and used over the years: - Hand-write a "Prism' MyTuple ByteString". This works, but is tedious and error-prone. - Use Serialize/Binary and trust that the encode/decode pair will produce results consistently in 5 years (dangerous territory!) - Use SafeCopy, which is great for ensuring timeless decoding of the *value* in the index, but can we be sure that fingerprint (MyTuple -> ByteString) conversion is persistent? What if SafeCopy authors one day decide to encode tuples differently? They would write the migrations to transparently handle legacy code for *values*, but not for *keys*. Also notice here how migrations help with the ByteString -> MyTuple leg, but do not ensure MyTuple -> ByteString produces the same ByteString over time. - Hashable would've been nice, but there is NO guarantee of persistent results, even across multiple runs of the same code What would be your preferred solution? Thank you, Oz