> I've seen interleaved lexing and parsing, where the recursive descent parser asks for the next token, which is computed on demand.

You even get this for free in a lazy language like Haskell, where your parser can accept a list of tokens `[Token]` whilst the list itself is only computed on-demand whenever the parser tries to get the next one.

Well, except for the context-sensitive option:

> (and as a consequence, it's natural to let lexing be context-sensitive where needed).