Magpie should allow defining of sentinel values in the library

[mrfoogles]

I read this blog post, which says that since Iterators and Channel.receive both behave in special ways with done, you are unable to put done in arrays. I agree that this is not a very common use case, but I think there's a better way to do it.

What you could define sentinel values in magpie? channel_done and iterator_done would both be sentinel values defined in the standard library. I think this fits magpie guide: the heart of magpie's parts about giving the user power and defining things in the library better as well.

I don't think this would be too hard to implement; just extend the code handling 'nothing' to any sentinel value. This might be possible regardless using fieldless classes, but it would be nice to have it work the same.

[munificent]

Not a bad idea, but I haven't touched Magpie in ten years. :)