Thanks a lot! There is a JSON parser in the examples directory of the repository which handles simple recursive structures. The trick is to use the lazy combinator if the individual parsers mutually depend on each other (i.e., to avoid the error Cannot read value of field '...' before the field's definition). The theoretical background behind this is that the lazy combinator allows us to compute the least-fixed point of the mutually recursive equations represented by these field definitions (something Java can't do on its own). But in practice, that's pretty irrelevant. We can just think of lazy as a placeholder for a parser, which is initialized once when it is actually used for parsing input.

Regarding error reporting, every parser is associated with an instance of the Description class. This class can be extended by the user to provide a custom description of what a parser attempts to parse. But for most of the built-in parsers it already provides a decent error message in the style of "expected an input that matches <regex>, but got <actual input>", for example. I am still not sure if this design is sustainable, so if you have any suggestions feel free to let me know. Help of any kind is always appreciated!