;;
;; Symbolic Regular Expressions
;;
;; For some sanity convert a symbolic regular expressions (sre) to
;; traditionl syntax.
;;
;; <string>             => that string in traditionl syntax
;; '<string>            => that string literal
;; ?x                   => that character literal
;; (and r1 ... rn)      =>  r1 ... rn
;; (or r1 ... rn)       =>  r1 | ... | rn
;; (1+ r)               =>  r+
;; (1- r)               =>  r?
;; (* r)                =>  r*
;; (= r)                =>  group capture
;;

(defun sre (x)
  (concat "\\(?:"
          (cond ((stringp x) x)
                ((eql x 't) ".")
                ((eql x ?\]) (string x))
                ((eql x ?^) "\\^")
                ((eql x ?-) (string x))
                ((characterp x) (concat "[" (string x) "]"))
                ((ecase (car x)
                   ((quote)
                    (let ((r ""))
                      (dotimes (i (length (cadr x)) r)
                        (setq r (concat r (sre (aref (cadr x) i)))))))
                   ((and)
                    (let ((r ""))
                      (dolist (k (cdr x) r)
                        (setq r (concat r (sre k))))))
                   ((or)
                    (let ((r nil))
                      (dolist (k (cdr x) r)
                        (setq r (if r (concat r "|" (sre k)) (sre k))))))
                   ((*)  (concat (sre `(and ,@(cdr x))) "*"))
                   ((1+) (concat (sre `(and ,@(cdr x))) "+"))
                   ((1-) (concat (sre `(and ,@(cdr x))) "?"))
                   ((=)  (concat "\\(" (sre `(and ,@(cdr x))) "\\)")))))
          "\\)"))