Hi,
I think this is my first post to this list although I've been reading it
for a long time. So, please, be patient with me and my post.
On 03/16/2010 02:29 PM, Louis Wasserman wrote:
* We offer Functor, Foldable, and Traversable instances that do not
respect key ordering. All are linear time, but Functor and
Traversable in particular assume the function is monotonic. The
Foldable instance is a good way to access the elements of the
priority queue in an unordered fashion. (We also export
mapMonotonic and traverseMonotonic, and encourage the use of those
functions instead of the Functor or Traversable instances.)
So, it is possible to break the invariants of your priority queue by
using fmap with a non-monotonic function, right? I see that it might be
usefull to have such instances, sometimes.
As it is not possible to hide instances, once they are definded, I'd
propose to not offer those instances by default. Instead you could
provide implementations of all the instance functions necessary to
define this instances yourself. Or one could have a newtype wrapper
around the priority queue for which instances of Function, Foldable, and
Traversable are defined. This would allow to "activate" the nice
instances on demand but to stay safe by default.
Best regards,
Jean-Marie
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