Advanced syntax-rules Techniques

Limitations of syntax-rules: it can't compute (e.g., concatenate identifiers into a new name like point-x) or break hygiene intentionally. Use syntax-case or er/ir macros for those.

;; 1. Accumulator style: build up results across recursive expansions
(define-syntax my-reverse-list
  (syntax-rules ()
    ((_ () (acc ...)) (list acc ...))
    ((_ (x rest ...) (acc ...)) (my-reverse-list (rest ...) (x acc ...)))))
(my-reverse-list (1 2 3) ())          ; (3 2 1)

;; 2. Vectors and dotted patterns
(define-syntax first-of-vector
  (syntax-rules () ((_ #(a b ...)) 'a)))
(first-of-vector #(x y z))            ; x

;; 3. Custom ellipsis (R7RS): escape ... or rename it to write macro-defining macros
(define-syntax def-alias
  (syntax-rules ()
    ((_ new old)
     (define-syntax new
       (syntax-rules ::: ()           ; use ::: as the ellipsis for the inner macro
         ((_ args :::) (old args :::)))))))
(def-alias plus +)
(plus 1 2 3)                          ; 6
;; (... ...) escapes an ellipsis inside a template

;; 4. Dispatching on internal keywords to structure expansion phases
(define-syntax my-define-record
  (syntax-rules ()
    ((_ name field ...)
     (begin
       (define (name field ...) (vector 'name field ...))))))

;; 5. Common macros worth writing
(define-syntax inc!
  (syntax-rules ()
    ((_ x) (set! x (+ x 1)))
    ((_ x n) (set! x (+ x n)))))

(d
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