> Try to write a parser for an arbitrarily complex and nested JSON object without running into runtime errors even after the fourth-or-so revision. Do you mean

> Try to write a parser for an arbitrarily complex and nested JSON object without running into runtime errors even after the fourth-or-so revision. Do you mean parsing the JSON bytes itself into maps and lists and atoms, or turning that into an application-useful object? If the former, are you claiming that Python's standard json library, libjansson, JSON::XS, etc. have bugs? (I don't know why you would roll your own JSON parser in production code.) If the latter, how are S-expressions any different? (And there are non-buggy libraries that do both, e.g., serde.)