Hello all, Can some one please suggest something on simulating some sort of "object-Ids" in Haskell? I mean, something like the following relation will hold:
a1 == a2 = (objectID a1) == (objectID a2)
Currently I have something like
import Data.Hash import qualified Data.ByteString.Char8 as B
newtype UniqueID = UniqueID (Hash, B.ByteString)
I have a type class called Identifiable, the instances of which are supposed to give a unqiue bytestring representation of the instance which can be arbitrarily long but should satisfy the condition mentioned earlier.
class Identifiable a where instanceID :: a -> B.ByteString
and finally, the required funtion objectID is defined as :
objectID :: (Hashable a, Identifiable a) => a -> UniqueID objectID a1 = UniqueID (hash a1, instanceID a1)
while comparing object Ids, I compare the hash values first (which can be faster for arbitrary values). Only if they are equal then I compare the instanceIDs and count on laziness for avoiding the construction of the bytestrings where they are not needed. Can you please suggest a better approach? I also toyed with the idea of storing all the data 'objects' in an array and use the index as the identifier but the trouble is I am not aware of all the number of instances before hand under all the circumstances. Many thanks Hemanth K