Question

How can I hash a string in haskell to get a more-or-less unique hash value. For example:

hash:: String -> Integer

>hash "foo"
1234123412
>hash "bar"
5938454

Or something along those lines? I’m not familiar with hashing in haskell so any help would be appreciated! Thanks.

Answer 1

You can use the hashable package from Hackage. It provides hash functions for a number of standard types, including strings:

Prelude Data.Hashable> hash "foo"
653367
Prelude Data.Hashable> hash "bar"
649056

If you want to implement your own, hash functions are usually easy to express as a fold. For example, here’s a variant of the DJB2 hash:

hash :: String -> Int
hash = foldl' (\h c -> 33*h `xor` fromEnum c) 5381

Note that these hash functions are meant to be simple and fast. If you’re looking for more complex hash functions, you can find a selection in the cryptohash package.