Yes, Regexp::Grammars basically just automates the same technique as demerphq's example uses: injection of a distributed stack-based tree-constructor via embedded code blocks.

But you really want that automation if the regex gets much more complex than the above example. Apart from the obvious maintainabilty issues of sprinkling dozens of (?{...}) blocks through your regex, there's a much more fundamental problem: if the regex can ever backtrack a repetition, that will almost certainly screw up the synchronization between the stack and the parser state, unless you take special precautions to unwind the stack correctly (which is what the module does for you).