Speaking of that Double instance... both data-binary and cereal use decodeFloat and encodeFloat which mean they suffer from the same problems as realToFrac, namely that -0 becomes 0 and NaN becomes -Infinity (I'm not sure why the latter happens since the decoded values differ... must be a problem with encodeFloat). It's tempting to just get the ieee754 bitmap out and serialize that. I know I've seen this question around before, but is it possible to somehow cast a D# directly to bytes? I know I can write a C function and FFI that in, but it would be tidier to do it all in haskell. I guess I can probably use castPtr and memCpy, but I don't see the required addressOf. I.e. how would I write 'memcpy(buf, &d, sizeof(double));'?
Also serialized data takes ~3 times more space than IEEE754 representation. It's a concern when a lot of data is serialized. Serialization in IEEE754 format is implemented already for binary. You can check package data-binary-ieee754[1] for [1] http://hackage.haskell.org/package/data-binary-ieee754