[Haskell-cafe] A distributed and replicating native Haskell database

[Joel Reymont]

Folks,

Allegro Common Lisp has AllegroCache [1], a database built on B-Trees  
that lets one store Lisp objects of any type. You can designate  
certain slots (object fields) as key and use them for lookup. ACL  
used to come bundled with the ObjectStore OODBMS for the same purpose  
but then adopted a native solution.

AllegroCache is not distributed or replicating but supports automatic  
versioning. You can redefine a class and new code will store more (or  
less) data in the database while code that uses the old schema will  
merrily chug along.

Erlang [2] has Mnesia [3] which lets you store any Erlang term  
("object"). It stores records (tuples, actually) and you can also  
designate key fields and use them for lookup. I haven't looked into  
this deeply but Mnesia is built on top of DETS (Disk-based Term  
Storage) which most likely also uses a form of B-Trees.

Mnesia is distributed and replicated in real-time. There's no  
automatic versioning with Mnesia but user code can be run to read old  
records and write new ones.

Would it make sense to build a similar type of a database for  
Haskell? I can immediately see how versioning would be much harder as  
Haskell is statically typed. I would love to extend recent gains in  
binary serialization, though, to add indexing of records based on a  
designated key, distribution and real-time replication.

What do you think?

To stimulate discussion I would like to ask a couple of pointed  
questions:

- How would you "designate" a key for a Haskell data structure?

- Is the concept of a schema applicable to Haskell?
	
	Thanks, Joel

[1] http://franz.com/products/allegrocache/index.lhtml
[2] http://erlang.org/faq/t1.html
[3] http://erlang.org/faq/x1409.html

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