RFC: Adding a Hashable type class and HashMap/HashSet data types to HP

[Thomas Schilling]

On 26 November 2010 17:18, Maciej Piechotka <uzytkownik2 at gmail.com> wrote:
> On Thu, 2010-11-25 at 16:15 +0000, Thomas Schilling wrote:
>> and for a data type with constructors C_1 .. C_n
>>
>>    2. hash (C_i x_i1 ... x_iN) = hash i <> hash x_i1 <> ... <> hash x_iN
>>
>> where <> is the hash combine function (probably (.))
>>
>
> (.) seems to fail type-checking.
>

Right, sorry, I was actually having a different type in mind.  Something like:

    newtype HashBuilder = HashBuilder { unHB :: Word -> Word }
    class Hashable a where
         addHash :: a -> HashBuilder

The argument would be the seed.  We'd then have:

    hash :: Hashable a => a -> Word
    hash a = finaliseHash $ unHB (addHash a) seed
       where
         seed = 0xdeadbeef
         finaliseHash x = ... -- some final mixing operation

As Bryan mentioned, though, this does not allow building hashes in
parallel.  It would also hard-code the hash function.

-- 
Push the envelope. Watch it bend.