I see that you've found an example of how recursive descent parsing actually can be implemented with the visitor pattern, which I've never come across before, and I didn't read it carefully enough to understand the motivation - but that doesn't mean they are the same thing - the recursive descent parsers I've seen before just inspect which tokens are seen and directly construct AST nodes
as an adendum, the reason I don't understand the motivation is that the visitor pattern in the way I described it is useful when you have many different operations to perform on your AST. If you have only one operation on tokens - parsing into an AST - I'm not sure why you need dynamic dispatch on a second thing, the first thing being the token type. Maybe the construction is that different operations correspond to different 'grammar rules'?
as an adendum, the reason I don't understand the motivation is that the visitor pattern in the way I described it is useful when you have many different operations to perform on your AST. If you have only one operation on tokens - parsing into an AST - I'm not sure why you need dynamic dispatch on a second thing, the first thing being the token type. Maybe the construction is that different operations correspond to different 'grammar rules'?