[barnacs]

If the fields of a structure or the string keys of an untyped map don't match then you don't have compatibility either way. The same is not true for restricting the set of valid values.

edit: To put it differently: To possibly be compatible with the nested "Circle" map, you need to know it is supposed to have a "Radius" key that is supposed to be a float. Type definitions just make this explicit. But just because your "Radius" can't be 0, you shouldn't make it incompatible with everything else operating on floats in general.