collections in hierarchical libraries

[Ross Paterson]

On Wed, Jan 14, 2004 at 10:38:15AM +0100, Daan Leijen wrote:
> No one seems to support Edison. However, there is an important
> difference between Edison and DData: DData provides implementations
> of specific structures, while Edison tried to provide general collection
> interfaces *and* implementations. I believe that designing good generic
> collection interfaces is very hard and may even be impossible to do "right"
> in current Haskell's. So, I guess we will be stuck with concrete
> data structures for a while :-)

It might be sensible to do the generic thing for sequences only:

* the generic interface is fairly clear (PreludeList + List + toList,
  fromList, empty, cons, snoc, lview, rview and a few others -- the only
  question is whether to reuse the standard names).

* the interface fits in Haskell 98, because element types are unconstrained.

* no implementation suits all purposes, and you often want to delay
  the choice.