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

[Maciej Piechotka]

On Fri, 2010-11-19 at 10:48 +0100, Gregory Collins wrote:
> On Thu, Nov 18, 2010 at 11:05 PM, Johan Tibell <johan.tibell at gmail.com> wrote:
> 
> > * A type class for things that can be hashed, Hashable.
> >
> > class Hashable a where
> >    hash :: a -> Word
> 

Shouldn't it be:

class Eq a => Hashable a where
	hash :: a -> Word

Or is there useful case where we want to hash something but it cannot be
member of Eq?

> BTW,
> 
> An issue that needs to be resolved is: "Where should this change go?" We have a
> couple of options:
> 
>   a) Bring http://hackage.haskell.org/package/hashable into the platform
> 
>   b) Put the module into base -- probably a -1 for political/logistical reasons
> 

I'd say base - there is Data.HashTable in base so adding function:

new' :: Hashable key => IO (HashTable key val)

would belong there

>   c) Put it into containers -- probably a -1 because it would force a
>      containers dependency where there was no containers dependency before.
> 
> Any other ideas?
> 
> G

Regards
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