Persistant (as in on disk) data

[Simon Marlow]

> a recent post reminded me of a feature i'd like.
> for all i know it is already implemenetd in GHC so pointers=20
> are welcome.
>=20
> i'd like to be able to dump data structures to disk, and later load=20
> them.

A Binary library was discussed recently on the libraries list.  The
thread starts here:

http://www.haskell.org/pipermail/libraries/2002-November/000691.html

It's currently stalled.  There are several implementations of Binary:
one that comes with NHC and is described in a paper (sorry, don't have a
link to hand), a port of this library to GHC by Sven Panne (suffers from
bitrot), a derived/simplified version used in GHC which is heavily
hacked for speed, and a further derived version of this library by Hal
Daume who is adapting it to support bit-by-bit serialisation.

I think the outstanding issues are

  (a) is the API for GHC's Binary library acceptable, or do we need
      the extra bells and whistles that the NHC version has?

  (b) can we make a version of Binary that uses a bit-by-bit
      rather than byte-by-byte serialisation of the data that is
      as fast (or nearly as fast) as the current byte-by-byte
      implementation?  Perhaps performance isn't that important
      to the majority of people: please comment if you have
      an opinion.

  (c) how do we derive instances of Binary?

IMHO: something is better than nothing, so I'd be in favour of just
plugging in the Binary library from GHC, and marking it "experimental".

Cheers,
	Simon