Aeson is built on the Show and Generic type classes. Anything that supports those also basically supports the FromJSON/ToJSON classes that Aeson needs. Lists al

Aeson is built on the Show and Generic type classes. Anything that supports those also basically supports the FromJSON/ToJSON classes that Aeson needs. Lists already support it (for types that also support aeson), as do Map/HashMap for various text types mapping to something that supports aeson. So, complex nested structures are a matter of defining Show and Generic instances for any types that don't already have them. From there you can trivially make those types aeson-compatible. Since so many common types are already supported, adding support for your own nested types isn't too difficult. The example use automatic derivation of Generic instances, which may result in some performance problems but is the easiest way to get off the ground.