;;;
;;; Outer "driver" macro; the meat is in pmatch-expand-pattern.
;;;
(define-syntax pmatch
  (syntax-rules ()
    ((pmatch value-expr (pattern . exprs) . clauses)
     (let* ((value value-expr)
            (try-next-clause
             (lambda () (pmatch value . clauses))))
       (pmatch-expand-pattern pattern
                              value
                              ;; success-k
                              (begin . exprs)
                              ;; failure-k
                              (try-next-clause))))))

(define-syntax pmatch-expand-pattern
  (lambda (stx)
    (syntax-case stx ()

      ;; Cases for constants and quoted symbols omitted, but they're trivial.

      ;; Match a pair pattern.  Note that failure-k is expanded three times;
      ;; that's why pmatch encapsulates its expansion inside a thunk!
      ((pmatch-expand-pattern (head-pat . tail-pat) value success-k failure-k)
       (syntax
        (if (pair? value)
            (pmatch-expand-pattern head-pat
                                   (car value)
                                   ;; If we successfully match the head, then
                                   ;; the success continuation is a recursive
                                   ;; attempt to match the tail...
                                   (pmatch-expand-pattern tail-pat
                                                          (cdr value)
                                                          success-k
                                                          failure-k)
                                   failure-k))
            failure-k))

      ;; Match an identifier pattern.  Always succeeds, binds identifier
      ;; to value
      ((pmatch-expand-pattern identifier value success-k failure-k)
       (identifier? (syntax identifier))
       (syntax (let ((identifier value)) success-k)))
      )))