I think this discussion is muddying the meanings of "recoverable" between "recoverable as a class" and "recoverable in this instance."
Parsing errors are recoverable as a class—you haven't irretrievably corrupted your process memory when you encounter one. Therefore, the parser itself should not panic(); it should just return an option type.
Parsing errors may very well be unrecoverable in a particular instance. The code calling the parser has every right to decide to unwrap() the option type such that a panic() will happen if the parse failed. The code calling the parser is likely business-logic code of an application, and is privy to knowledge like "if there is no configuration supplied here, then later code that tries to consume the configuration will have to crash" and so can decide to early-exit with a user-comprehensible error ("you don't have a config file!") rather than letting the later code crash with some weird error about a config value being Nothing.
