When to Use Maybe

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Maybe can be used:

1. in the data representation
2. in what the data accessors return

So we'd have HasX classy-lenses and MayHaveX classy-lenses. We could have instances of MayHaveX for all sorts of things where we already know there is no X but where asking the question isn't silly. We do need to be careful to not implement MayHaveX where the question should not be asked.

From the point of view of our usage, lenses are just polymorphic getters. We want to be able to "get X" from some representation without caring how X is embedded in the data we've been handed, as long as we're promised that X is in there somewhere.