Re: [Haskell-cafe] What is the meaning of tilde ("~") symbol

On Sun, Feb 14, 2010 at 2:22 PM, Stephen Tetley wrote:

On 14 February 2010 22:11, Evan Laforge wrote:

...

There's still no consensus on typeclasses for collections, so these are all separate functions.  Has anyone taken a shot at a set of AT-using classes for the standard collections?

The standard collections have different shapes depending on what they represent (maps, trees, lists, sequences) so considering Functor, Traversable, Foldable perhaps the common operations are largely already covered. A unifying 'collection' class might be as problematic as good old Num is for numbers...

But how about indexing? It would be nice to have universal operators like (!!) :: collection elt -> index -> elt lookup :: index -> collection elt -> Maybe elt member :: index -> collection elt -> Bool That way you can have nice short names for these common operations. Lists are very flexible but it's nothing Monoid hasn't already done with integers and newtype wrappers, and there are plenty of others which would be applicable (no pun intended): Map, Set, Bytestring, Sequence. I suppose we can get empty and concat with Monoid. What about singleton? The names and locations are all over the map (no really, not intended) too, symptomatic I suppose of the fact that they all evolved separately.