I have recently completed two major projects that were taking up nearly all of my time. Now that they are done, I'd like to work on the next version of the iteratee package. Here are a few ideas that I hope to include soon.
1. Remove the explicit Maybes
This was suggested by Oleg, and it seems to be a good idea. Every iteratee that produces a value other than () uses Maybe to represent the possibility of failure (always an option when doing IO). By incorparating the Maybe into the type of IterateeG, these will no longer need to be explicit. This will also make IterateeGM an instance of MonadZero to the extent that Maybe is an instance of that class.
Status: I've made a patch that does this, but it doesn't yet work properly with convStream. I haven't managed to track down the problem. Likely to be included, assuming I can solve this issue in a reasonable time frame.
2. Stream type class (and simplify StreamChunk)
I keep hoping for a ListLike type class to enter common use. Barring that, I have some ideas for breaking up the necessary functions of StreamChunk into separate type classes, such as the patch to use a monoid instance submitted by Bas van Dijk.
Status: Changes will be made, it is likely that StreamChunk will be broken into multiple smaller classes. Any addition of a Stream type class will wait until after point 4 is resolved.
3. More utility iteratees (foldl, filter, others?)
Status: Likely to be included. Changes to StreamChunk will make these easier to support.
4. Type-safe seeking
If iteratees are parameterized by Stream, the type of the stream should indicate if seeking is supported. I have an outline for how to implement this, but haven't done any work yet.
Status: Needs research, this will probably wait for the next major version bump.
5. Improved error handling
Bas van Dijk submitted a patch to change the type of a stream error from String to Error a. Others have suggested other possible changes as well.
Status: Needs more research, this will likely wait for the next major version bump.