On Fri, Mar 19, 2010 at 10:52:10AM +0100, Stephan Friedrichs wrote:
On 17/03/10 16:47, Ross Paterson wrote:
On Tue, Mar 16, 2010 at 08:54:15AM -0500, Louis Wasserman wrote:
A couple potentially contentious design decisions:
* There is no distinction between keys and priority values. A utility type Prio p a with the instance Ord p => Ord (Prio p a) is exported to allow usage of distinct keys and priority values.
I disagree with this one. It requires an Ord instance that isn't really an ordering, and makes a Functor instance impossible. I would prefer an interface separating keys and values like that of Data.Map (which would also increase consistency within the package).
I agree. The Functor instance is crucial (at least to me). Besides, I'm the author of [1] and writing that package, I made the experience that it absolutely makes sense to separate the part of a queue entry that determines it's position within the queue from the part that is user data. A clean Functor instance is just one of the benefits.
For a containers-compatible interface (ignoring the implementation), see http://hackage.haskell.org/packages/archive/fingertree/0.0.1.0/doc/html/Data...
* I'm not comfortable with having two redundant modules, one for Min- and one for MaxQueue. It is possible to implement both in the same data structure and still get type errors when e.g. 'union' on a Min- and a MaxQueue (I did that in [1], please have a look at the latest version). My solution needs type families, which would not be good for containers, but I'm pretty sure there's a containers-compatible solution.
If keys are separate, the two versions could be easily achieved using an inversion adaptor on Ord, which has been proposed before and would have many other uses.