[Haskell-cafe] Purely Functional Data Structures

[Jeremy Shaw]

At Sun, 08 Mar 2009 00:13:14 +0100,
G?uenther Schmidt wrote:
> In SQL I would have the data indexed by several 
> different columns, if I use maps I'd only have one key, so if I need to 
> lookup data in the map by a value that is not the key the lookups will 
> become quite expensive.

happstack-ixset offers a data-type similar to Map except that you can
have multiple keys. You can even have keys that are calculated from
the data but don't actually appear in the data itself. For, example,
if your ixset just contains Strings, one of the keys could be the
length of the String.

happstack-ixset (and its dependencies) also offers compact
serialization/deserialization of the ixset to disk, data migration
options, and a smattering of other features that may or may not be
useful to you.

While happstack-ixset is built to work with happstack, it is does not
depend on the happstack http server or persistent store layer, so it
should be useful even if you are not being an application server.

- jeremy