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

On Sat, Nov 20, 2010 at 3:53 PM, Maciej Piechotka wrote:

On Fri, 2010-11-19 at 10:48 +0100, Gregory Collins wrote:

...

On Thu, Nov 18, 2010 at 11:05 PM, Johan Tibell 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?

I can think of a few. Regardless, constraining the type class in this way doesn't really buy us anything. Johan