RFC: Adding a Hashable type class and HashMap/HashSet data
types to HP
uzytkownik2 at gmail.com
Sat Nov 20 09:53:03 EST 2010
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?
> 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?
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