[Haskell-cafe] mapping unfreeze over an IntMap of IOUArrays

[Don Stewart]

bulat.ziganshin:
> Hello Don,
> 
> Wednesday, November 12, 2008, 12:51:33 AM, you wrote:
> 
> >> btw, i made here some time ago proposal about pure hashtables
> 
> > Did you end up implementing this?
> 
> yes, i have published here all the 10 lines of implementation :)))
> 
> citing letter to you:
> 
> actually, writing HT module from scratch is
> very easy - all we need is a prime searching function (in order to
> establish array size). everything else:
> 
> data HT a b = HT (a->Int) (Array Int [(a,b)])
> 
> -- size is the size of array (we implent closed hash)
> -- hash is the hash function (a->Int)
> -- list is assoclist of items to put in hash
> create size hash list = HT hashfunc
>                            (accumArray (flip (:))
>                                        []
>                                        (0, arrsize-1)
>                                        (map (\(a,b) -> (hashfunc a,b)) list)
>                            )
> 
>   where arrsize     =  head$ filter (>size)$ iterate (\x->3*x+1) 1
>         hashfunc a  =  hash a `mod` arrsize
> 
> 
> lookup a (HT hash arr) = List.lookup a (arr!hash a)
> 
> 
> example:
> 
> main = do let assoclist = [("one", 1), ("two", 2), ("three", 3)]
>               hash = HT.create 10 Data.HashTable.hashString assoclist
>           print (HT.lookup "one" hash)
>           print (HT.lookup "zero" hash)
> 
> 

If this structure is useful, you should release it on Hackage.
You've not tested the performance though, I imagine, versus
say, hasing into an IntMap?

-- Don