I’ve just submitted a Functional Pearl to ICFP explaining combinatorial species in a way that is (hopefully) accessible and interesting to functional programmers. You can read the draft here — as always, comments, suggestions, etc. are welcome (although it’s too late to help my ICFP chances =).
I plan to upload a new version of my species library soon with a ton of major improvements (unlabelled enumeration, and automatically deriving species corresponding to user-defined data types via Template Haskell, to name a couple). When I do I’ll be sure to write about it here!
Also, the paper doesn’t mention it, but all the diagrams in the paper were of course generated with diagrams.
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I don’t understand why fmap and enumerate for Zero must be undefined. Couldn’t you have fmap _ = id and enumerate _ = [] ? The fmap seems to be mostly philosophical, since you’ll never find anything to apply it to, but don’t you need to define enumerate in order to use Zero in sums?
Ah, thanks, you’re absolutely right, enumerate for Zero ought to be enumerate _ = []. That’s what I get for not actually running the code!
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