Comment by mrgriffin
6 years ago
I'm pretty confident that you could write something that was equivalent to all the useful `pickle` calls. By that I mean you'll need to know which operations you'll want to do on your unpickled object:
readAny :: forall c r. [TypeWithReadAnd c] -> String -> (forall a. c a => a -> r) -> Maybe r
readAny types string handle
I think it's fair to say "hey, pickle doesn't require me to list all my types explicitly", but on the other hand, it's not like pickle can conjure those types out of thin air--it considers only the types that are defined in your program.
Here's an example that uses Read as the serialization format and only deals with Int, Char and String; but hopefully you can imagine that I could replace the use of read with a per-type function that deserializes from a byte string or whatever.
IIRC the pickle format can define new classes, but I haven't looked at it in over a decade so I might be misremembering.
You might be right, it's been a long time for me too. But if it can define new classes, then I'd expect that the code for those classes' methods would also be in the pickled format, at which point there's no particular reason you couldn't deserialize it in Haskell too... with some caveats about either needing to know what types those functions should have, or needing to build a run-time representation of those types so that they can be checked when called, or (hopefully!) crashing if you're okay with just unsafeCoercing things around.