CODEWITHSUNDEEP
haskellserializationtypes
jberryman
jberryman

Reputation: 16645

Serialisable stable representation of a type

I'm working on a data structure that I would like to serialize, with an API like:

serialize :: Foo a -> ByteString
deserialize :: ByteString -> Maybe (Foo a)

In my case a is a phantom parameter; there are no values in Foo to witness that type, but preserving the type is important.

GHC provides Typeable which can give me a TypeRep form which I can extract a Fingerprint , but I don't believe that representation is necessarily stable across different architectures and versions of GHC.

Is there some way I can reliably serialize a type representation, perhaps with the new static pointers thing, or something else in base?

EDIT: I've implemented this type versioning functionality (sort of "hashing of types") in hashabler; see TypeHash.

Upvotes: 3

Views: 126

Answers (1)

dfeuer
dfeuer

Reputation: 48611

You might be able to play games with Typeable, as the binary-typed package does. It allows you to remove and reconstruct fingerprints as needed. I'm not sure if that will work for types manufactured on the fly. Another option is to manufacture some tags yourself, as long as you know or can figure out which values have the same phantoms. An extreme approach might be to build a Map of the TypeReps you see along the way, mapping them to unique Int values. On the other end, you can make an IntMap from the tags to functions that wrap up the values properly.

Upvotes: 2

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