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> just inspect which tokens are seen and directly construct AST nodes

I'll repeat myself: this is not possible because you need to recursively construct the nodes (how else would you get a tree...).

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I think I'm missing something here. if you have a grammar rule R with children A and B, and a function in your recursive descent parser that corresponds to R, why can R not call the parser functions for A and B, which return AST nodes themselves, and then construct another AST node using the result of those? Where was the visitor pattern required here?

Me too. No-one's denying that recursion is happening. We're just not sure about it being synonymous with the Visitor Pattern.

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