[Haskell-cafe] Inecxact map?

[Morten Olsen Lysgaard]

I'm running a project where i want to generate a map of a rather large 
data collection. The map is if the form: Data.Map.Map String a
I'd like to be able to do inexact lookups on the map. Firstly, ignore 
the difference between upper lower case, that's easy. But secondly, have 
a function:

search :: (Num b) => Data.Map.Map String a -> String -> b -> [a]

This function is like the normal lookup, but it takes an extra argument 
b. B is the allowed character error rate. That is the Levenstein 
distance divided on the length. It should return all the strings that 
has an error rate lower that b and in a ordered manner, best first.

Is it possible to design such a datastructure efficiently?
Does there already exist something like this?
If not, where would i begin to create this?

Any advices or knowledge appreciated.

-- 
Morten