A working but not recommended macro

syntax-rules-ex.scm

;;; This is not a good use of macros. See below for an
;;; example implementation of COND.

(define-syntax proc-all
  (syntax-rules ()
    ((_ exp () body ...)
     (begin body ...))
    ((_ exp (match matches ...) body ...)
     (unless (= exp match) (proc-all exp (matches ...) body ...)))))

;;; Example

(proc-all 4 (3 2 1) (display "4 is not 3, 2, or 1.") (newline))
;; Prints the message.

(proc-all 2 (3 2 1) (display "4 is not 3, 2, or 1.") (newline))
;; Does not print the message.

;;; Something less crazy (COND including ELSE and => features)

(define-syntax my-cond
  (syntax-rules (else =>)
    ((_) (begin))
    ((_ (else body ...)) (begin body ...))
    ((_ (test => proc) clauses ...)
     (let ((result test))
       (if result
           (proc result)
           (my-cond clauses ...))))
    ((_ (test body ...) clauses ...)
     (if test (begin body ...)
         (my-cond clauses ...)))))