>> Is Pointed useful at all? The last time this discussion came up, I
>> asked for algorithms which were generic over pointed functors (in the
>> same way that traverse is generic over applicative functors) and no
>> one could think of any.
>
> It's useful for 'singleton' on probabilistic data structures (e.g. a Bloom
> filter).
Again, I'm asking for clients, not implementations. Are there any
useful, non-trivial functions which are parameterized by arbitrary
Pointed functors?
I consider "singleton" itself to be a client, albeit somewhat trivial. But as a result of the last discussion, I'm no longer sure that "singleton" is a proper use of "pointed" and I shouldn't have brought it up now. I'm still in favor of splitting Applicative for philosophical reasons though.
In any case there's the function posted by Ross Patterson, which seems to fit all your criteria.
John