[bmh100]

This seems to me like a very practical way to approach Clojure typing. Similar to the author, I have often needed to make a series of transformations on complex objects. Those transformations mostly depended on the presence of certain keys, so having strict types was unnecessarily rigid. Derived typing would also be useful, of course.

One point to appreciate about this approach is the flexibility in only worrying about the relevant pieces. In my case, I may be worrying about whether a continuous variable has been tagged "datetime", requiring additional processing steps. Merely checking for such tags allows the input data to implicitly direct the flow of the program, reducing the coupling between data and specific processing implementations.