The final `syntax-case` version:

    (define-syntax (nest stx)
      (syntax-case stx ()
        ((nest outer ... inner)
         (foldr (lambda (o i)
                  (with-syntax (((outer ...) o)
                                 (inner i))
                    #'(outer ... inner)))
                #'inner (syntax->list #'(outer ...))))))

looks fine to me. Using #` and #, and defining `reduce` one could make a version that looks like the Common Lisp implementation.

Note that the `nest` form just rearranges its input - so there is no problems getting the scope of identifiers correct. That is: we are well within the comfort zone of `defmacro`.

With regards to the `syntax-rules` solution: Fare refers to "when I learned Scheme" and pre-R6RS there were no `syntax-case` in the specification. In practise all implemenations did have macro systems more expressive than `syntax-rules`, but it was fun to see whether something was possible with plain `syntax-rules`.

Right, it's fine, and is a pretty basic macro. Doubly linked lists are pretty basic data structures too, even the Rust versions once you figure it out. I like your sibling comment making it look like the CL version. I still want to know in more detail though why you think that doing things this way instead of the CL way is less likely to be "fragile and break down" for the complicated stuff, it would help to have a specific complicated example to showcase. Perhaps the linked https://github.com/disconcision/fructure in another comment would be a good study? The author there claimed they might not have been able to manage with defmacro, maybe someone familiar with both could articulate the challenges in detail. Is it just an issue of some things benefit a lot from pattern matching, and if so, does using CL's Trivia system mitigate that at all (in the same way that using gensym+packages+Lisp-2ness can mitigate hygiene issues)? Or is it more when there's a point of complexity where you need to do code walking, and this is more straightforward in something like Racket?