irregex.scm

;;;; irregex.scm -- IrRegular Expressions
;;
;; Copyright (c) 2005-2024 Alex Shinn.  All rights reserved.
;; BSD-style license: http://synthcode.com/license.txt

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; At this moment there was a loud ring at the bell, and I could
;; hear Mrs. Hudson, our landlady, raising her voice in a wail of
;; expostulation and dismay.
;;
;; "By heaven, Holmes," I said, half rising, "I believe that
;; they are really after us."
;;
;; "No, it's not quite so bad as that.  It is the unofficial
;; force, -- the Baker Street irregulars."

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Notes
;;
;; This code should not require any porting - it should work out of
;; the box in any R[457]RS Scheme implementation.  Slight modifications
;; are needed for R6RS (a separate R6RS-compatible version is included
;; in the distribution as irregex-r6rs.scm).
;;
;; The goal of portability makes this code a little clumsy and
;; inefficient.  Future versions will include both cleanup and
;; performance tuning, but you can only go so far while staying
;; portable.  AND-LET*, SRFI-9 records and custom macros would've been
;; nice.

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; History
;; 0.9.11: 2024/02/23 - Guile test and packaging support from Tomas Volf.
;; 0.9.10: 2021/07/06 - fixes for submatches under kleene star, empty seqs
;;                     in alternations, and bol in folds for backtracking
;;                     matcher (thanks John Clements and snan for reporting
;;                     and Peter Bex for fixing)
;; 0.9.9: 2021/05/14 - more comprehensive fix for repeated empty matches
;; 0.9.8: 2020/07/13 - fix irregex-replace/all with look-behind patterns
;; 0.9.7: 2019/12/31 - more intuitive handling of empty matches in -fold,
;;                     -replace and -split
;; 0.9.6: 2016/12/05 - fixed exponential memory use of + in compilation
;;                     of backtracking matcher (CVE-2016-9954).
;; 0.9.5: 2016/09/10 - fixed a bug in irregex-fold handling of bow
;; 0.9.4: 2015/12/14 - performance improvement for {n,m} matches
;; 0.9.3: 2014/07/01 - R7RS library
;; 0.9.2: 2012/11/29 - fixed a bug in -fold on conditional bos patterns
;; 0.9.1: 2012/11/27 - various accumulated bugfixes
;; 0.9.0: 2012/06/03 - Using tags for match extraction from Peter Bex.
;; 0.8.3: 2011/12/18 - various accumulated bugfixes
;; 0.8.2: 2010/08/28 - (...)? submatch extraction fix and alternate
;;                     named submatches from Peter Bex
;;                     Added irregex-split, irregex-extract,
;;                     irregex-match-names and irregex-match-valid-index?
;;                     to Chicken and Guile module export lists and made
;;                     the latter accept named submatches.  The procedures
;;                     irregex-match-{start,end}-{index,chunk} now also
;;                     accept named submatches, with the index argument
;;                     made optional.  Improved argument type checks.
;;                     Disallow negative submatch index.
;;                     Improve performance of backtracking matcher.
;;                     Refactor charset handling into a consistent API
;; 0.8.1: 2010/03/09 - backtracking irregex-match fix and other small fixes
;; 0.8.0: 2010/01/20 - optimizing DFA compilation, adding SRE escapes
;;                     inside PCREs, adding utility SREs
;; 0.7.5: 2009/08/31 - adding irregex-extract and irregex-split
;;                     *-fold copies match data (use *-fold/fast for speed)
;;                     irregex-opt now returns an SRE
;; 0.7.4: 2009/05/14 - empty alternates (or) and empty csets always fail,
;;                     bugfix in default finalizer for irregex-fold/chunked
;; 0.7.3: 2009/04/14 - adding irregex-fold/chunked, minor doc fixes
;; 0.7.2: 2009/02/11 - some bugfixes, much improved documentation
;; 0.7.1: 2008/10/30 - several bugfixes (thanks to Derick Eddington)
;; 0.7.0: 2008/10/20 - support abstract chunked strings
;; 0.6.2: 2008/07/26 - minor bugfixes, allow global disabling of utf8 mode,
;;                     friendlier error messages in parsing, \Q..\E support
;; 0.6.1: 2008/07/21 - added utf8 mode, more utils, bugfixes
;;   0.6: 2008/05/01 - most of PCRE supported
;;   0.5: 2008/04/24 - fully portable R4RS, many PCRE features implemented
;;   0.4: 2008/04/17 - rewriting NFA to use efficient closure compilation,
;;                     normal strings only, but all of the spencer tests pass
;;   0.3: 2008/03/10 - adding DFA converter (normal strings only)
;;   0.2: 2005/09/27 - adding irregex-opt (like elisp's regexp-opt) utility
;;   0.1: 2005/08/18 - simple NFA interpreter over abstract chunked strings

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Data Structures

(define irregex-tag '*irregex-tag*)

(define (make-irregex dfa dfa/search nfa flags submatches lengths names)
  (vector irregex-tag dfa dfa/search nfa flags submatches lengths names))

(define (irregex? obj)
  (and (vector? obj)
       (= 8 (vector-length obj))
       (eq? irregex-tag (vector-ref obj 0))))

(define (irregex-dfa x) (vector-ref x 1))
(define (irregex-dfa/search x) (vector-ref x 2))
(define (irregex-nfa x) (vector-ref x 3))
(define (irregex-flags x) (vector-ref x 4))
(define (irregex-num-submatches x) (vector-ref x 5))
(define (irregex-lengths x) (vector-ref x 6))
(define (irregex-names x) (vector-ref x 7))

(define (vector-copy v)
  (let ((r (make-vector (vector-length v))))
    (do ((i (- (vector-length v) 1) (- i 1)))
        ((< i 0) r)
      (vector-set! r i (vector-ref v i)))))

(define (irregex-new-matches irx)
  (make-irregex-match (irregex-num-submatches irx) (irregex-names irx)))

(define (irregex-reset-matches! m)
  (do ((i (- (vector-length m) 1) (- i 1)))
      ((<= i 3) m)
    (vector-set! m i #f)))

(define (irregex-copy-matches m)
  (and (vector? m) (vector-copy m)))

(define irregex-match-tag '*irregex-match-tag*)

(define (irregex-match-data? obj)
  (and (vector? obj)
       (>= (vector-length obj) 11)
       (eq? irregex-match-tag (vector-ref obj 0))))

(define (make-irregex-match count names)
  (let ((res (make-vector (+ (* 4 (+ 2 count)) 3) #f)))
    (vector-set! res 0 irregex-match-tag)
    (vector-set! res 2 names)
    res))

(define (irregex-match-num-submatches m)
  (- (quotient (- (vector-length m) 3) 4) 2))

(define (irregex-match-chunker m)
  (vector-ref m 1))
(define (irregex-match-names m)
  (vector-ref m 2))
(define (irregex-match-chunker-set! m str)
  (vector-set! m 1 str))

(define (%irregex-match-start-chunk m n) (vector-ref m (+ 3 (* n 4))))
(define (%irregex-match-start-index m n) (vector-ref m (+ 4 (* n 4))))
(define (%irregex-match-end-chunk m n)   (vector-ref m (+ 5 (* n 4))))
(define (%irregex-match-end-index m n)   (vector-ref m (+ 6 (* n 4))))

(define (%irregex-match-fail m)
  (vector-ref m (- (vector-length m) 1)))
(define (%irregex-match-fail-set! m x)
  (vector-set! m (- (vector-length m) 1) x))

;; public interface with error checking
(define (irregex-match-start-chunk m . opt)
  (let ((n (irregex-match-numeric-index "irregex-match-start-chunk" m opt)))
    (and n (%irregex-match-start-chunk m n))))
(define (irregex-match-start-index m . opt)
  (let ((n (irregex-match-numeric-index "irregex-match-start-index" m opt)))
    (and n (%irregex-match-start-index m n))))
(define (irregex-match-end-chunk m . opt)
  (let ((n (irregex-match-numeric-index "irregex-match-end-chunk" m opt)))
    (and n (%irregex-match-end-chunk m n))))
(define (irregex-match-end-index m . opt)
  (let ((n (irregex-match-numeric-index "irregex-match-end-index" m opt)))
    (and n (%irregex-match-end-index m n))))

(define (irregex-match-start-chunk-set! m n start)
  (vector-set! m (+ 3 (* n 4)) start))
(define (irregex-match-start-index-set! m n start)
  (vector-set! m (+ 4 (* n 4)) start))
(define (irregex-match-end-chunk-set! m n end)
  (vector-set! m (+ 5 (* n 4)) end))
(define (irregex-match-end-index-set! m n end)
  (vector-set! m (+ 6 (* n 4)) end))

;; Tags use indices that are aligned to start/end positions just like the
;; match vectors.  ie, a tag 0 is a start tag, 1 is its corresponding end tag.
;; They start at 0, which requires us to map them to submatch index 1.
;; Sorry for the horrible name ;)
(define (irregex-match-chunk&index-from-tag-set! m t chunk index)
  (vector-set! m (+ 7 (* t 2)) chunk)
  (vector-set! m (+ 8 (* t 2)) index))

;; Helper procedure to convert any type of index from a rest args list
;; to a numeric index.  Named submatches are converted to their corresponding
;; numeric index, and numeric submatches are checked for validity.
;; An error is raised for invalid numeric or named indices, #f is returned
;; for defined but nonmatching indices.
(define (irregex-match-numeric-index location m opt)
  (cond
   ((not (irregex-match-data? m))
    (error (string-append location ": not match data") m))
   ((not (pair? opt)) 0)
   ((pair? (cdr opt))
    (apply error (string-append location ": too many arguments") m opt))
   (else
    (let ((n (car opt)))
      (if (number? n)
          (if (and (integer? n) (exact? n))
              (if (irregex-match-valid-numeric-index? m n)
                  (and (irregex-match-matched-numeric-index? m n) n)
                  (error (string-append location ": not a valid index")
                         m n))
              (error (string-append location ": not an exact integer") n))
          (let lp ((ls (irregex-match-names m))
                   (unknown? #t))
            (cond
             ((null? ls)
              (and unknown?
                   (error (string-append location ": unknown match name") n)))
             ((eq? n (caar ls))
              (if (%irregex-match-start-chunk m (cdar ls))
                  (cdar ls)
                  (lp (cdr ls) #f)))
             (else (lp (cdr ls) unknown?)))))))))

(define (irregex-match-valid-numeric-index? m n)
  (and (>= n 0) (< (+ 3 (* n 4)) (- (vector-length m) 4))))

(define (irregex-match-matched-numeric-index? m n)
  (and (vector-ref m (+ 4 (* n 4)))
       #t))

(define (irregex-match-valid-named-index? m n)
  (and (assq n (irregex-match-names m))
       #t))

(define (irregex-match-valid-index? m n)
  (if (not (irregex-match-data? m))
      (error "irregex-match-valid-index?: not match data" m))
  (if (integer? n)
      (if (not (exact? n))
          (error "irregex-match-valid-index?: not an exact integer" n)
          (irregex-match-valid-numeric-index? m n))
      (irregex-match-valid-named-index? m n)))

(define (irregex-match-substring m . opt)
  (let* ((n (irregex-match-numeric-index "irregex-match-substring" m opt))
         (cnk (irregex-match-chunker m)))
    (and n
         ((chunker-get-substring cnk)
          (%irregex-match-start-chunk m n)
          (%irregex-match-start-index m n)
          (%irregex-match-end-chunk m n)
          (%irregex-match-end-index m n)))))

(define (irregex-match-subchunk m . opt)
  (let* ((n (irregex-match-numeric-index "irregex-match-subchunk" m opt))
         (cnk (irregex-match-chunker m))
         (get-subchunk (chunker-get-subchunk cnk)))
    (if (not get-subchunk)
        (error "this chunk type does not support match subchunks")
        (and n (get-subchunk
                (%irregex-match-start-chunk m n)
                (%irregex-match-start-index m n)
                (%irregex-match-end-chunk m n)
                (%irregex-match-end-index m n))))))

;; chunkers tell us how to navigate through chained chunks of strings

(define (make-irregex-chunker get-next get-str . o)
  (let* ((get-start (or (and (pair? o) (car o)) (lambda (cnk) 0)))
         (o (if (pair? o) (cdr o) o))
         (get-end (or (and (pair? o) (car o))
                      (lambda (cnk) (string-length (get-str cnk)))))
         (o (if (pair? o) (cdr o) o))
         (get-substr
          (or (and (pair? o) (car o))
              (lambda (cnk1 start cnk2 end)
                (if (eq? cnk1 cnk2)
                    (substring (get-str cnk1) start end)
                    (let loop ((cnk (get-next cnk1))
                               (res (list (substring (get-str cnk1)
                                                     start
                                                     (get-end cnk1)))))
                      (if (eq? cnk cnk2)
                          (string-cat-reverse
                           (cons (substring (get-str cnk)
                                            (get-start cnk)
                                            end)
                                 res))
                          (loop (get-next cnk)
                                (cons (substring (get-str cnk)
                                                 (get-start cnk)
                                                 (get-end cnk))
                                      res))))))))
         (o (if (pair? o) (cdr o) o))
         (get-subchunk (and (pair? o) (car o))))
    (if (not (and (procedure? get-next) (procedure? get-str)
                  (procedure? get-start) (procedure? get-substr)))
        (error "make-irregex-chunker: expected a procdure"))
    (vector get-next get-str get-start get-end get-substr get-subchunk)))

(define (chunker-get-next cnk) (vector-ref cnk 0))
(define (chunker-get-str cnk) (vector-ref cnk 1))
(define (chunker-get-start cnk) (vector-ref cnk 2))
(define (chunker-get-end cnk) (vector-ref cnk 3))
(define (chunker-get-substring cnk) (vector-ref cnk 4))
(define (chunker-get-subchunk cnk) (vector-ref cnk 5))

(define (chunker-prev-chunk cnk start end)
  (if (eq? start end)
      #f
      (let ((get-next (chunker-get-next cnk)))
        (let lp ((start start))
          (let ((next (get-next start)))
            (if (eq? next end)
                start
                (and next (lp next))))))))

(define (chunker-prev-char cnk start end)
  (let ((prev (chunker-prev-chunk cnk start end)))
    (and prev
         (string-ref ((chunker-get-str cnk) prev)
                     (- ((chunker-get-end cnk) prev) 1)))))

(define (chunker-next-char cnk src)
  (let ((next ((chunker-get-next cnk) src)))
    (and next
         (string-ref ((chunker-get-str cnk) next)
                     ((chunker-get-start cnk) next)))))

(define (chunk-before? cnk a b)
  (and (not (eq? a b))
       (let ((next ((chunker-get-next cnk) a)))
         (and next
              (if (eq? next b)
                  #t
                  (chunk-before? cnk next b))))))

;; For look-behind searches, wrap an existing chunker such that it
;; returns the same results but ends at a given point.
(define (wrap-end-chunker cnk src i)
  (make-irregex-chunker
   (lambda (x) (and (not (eq? x src)) ((chunker-get-next cnk) x)))
   (chunker-get-str cnk)
   (chunker-get-start cnk)
   (lambda (x)
     ;; TODO: this is a hack workaround for the fact that we don't
     ;; have either a notion of chunk equivalence or chunk truncation,
     ;; until which time (neg-)look-behind in a fold won't work on
     ;; non-basic chunks.
     (if (or (eq? x src)
             (and (not ((chunker-get-next cnk) x))
                  (not ((chunker-get-next cnk) src))))
         i
         ((chunker-get-end cnk) x)))
   (chunker-get-substring cnk)
   (chunker-get-subchunk cnk)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; String Utilities

;; Unicode version (skip surrogates)
(define *all-chars*
  `(/ ,(integer->char 0) ,(integer->char #xD7FF)
      ,(integer->char #xE000) ,(integer->char #x10FFFF)))

;; ASCII version, offset to not assume 0-255
;; (define *all-chars* `(/ ,(integer->char (- (char->integer #\space) 32)) ,(integer->char (+ (char->integer #\space) 223))))

;; set to #f to ignore even an explicit request for utf8 handling
;; The utf8-mode is undesired on any implementation with native unicode support.
;; It is a workaround for those that treat strings as a raw byte sequences, and
;; does not work well otherwise.  So disable it on implementations known to
;; handle unicode natively.
(define *allow-utf8-mode?* (cond-expand ((and chicken (not full-unicode)) #t)
                                        (else #f)))

;; (define *named-char-properties* '())

(define (string-scan-char str c . o)
  (let ((end (string-length str)))
    (let scan ((i (if (pair? o) (car o) 0)))
      (cond ((= i end) #f)
            ((eqv? c (string-ref str i)) i)
            (else (scan (+ i 1)))))))

(define (string-scan-char-escape str c . o)
  (let ((end (string-length str)))
    (let scan ((i (if (pair? o) (car o) 0)))
      (cond ((= i end) #f)
            ((eqv? c (string-ref str i)) i)
            ((eqv? c #\\) (scan (+ i 2)))
            (else (scan (+ i 1)))))))

(define (string-scan-pred str pred . o)
  (let ((end (string-length str)))
    (let scan ((i (if (pair? o) (car o) 0)))
      (cond ((= i end) #f)
            ((pred (string-ref str i)) i)
            (else (scan (+ i 1)))))))

(define (string-split-char str c)
  (let ((end (string-length str)))
    (let lp ((i 0) (from 0) (res '()))
      (define (collect) (cons (substring str from i) res))
      (cond ((>= i end) (reverse (collect)))
            ((eqv? c (string-ref str i)) (lp (+ i 1) (+ i 1) (collect)))
            (else (lp (+ i 1) from res))))))

(define (char-alphanumeric? c)
  (or (char-alphabetic? c) (char-numeric? c)))

(define (%substring=? a b start1 start2 len)
  (let lp ((i 0))
    (cond ((>= i len)
           #t)
          ((char=? (string-ref a (+ start1 i)) (string-ref b (+ start2 i)))
           (lp (+ i 1)))
          (else
           #f))))

;; SRFI-13 extracts

(define (%%string-copy! to tstart from fstart fend)
  (do ((i fstart (+ i 1))
       (j tstart (+ j 1)))
      ((>= i fend))
    (string-set! to j (string-ref from i))))

(define (string-cat-reverse string-list)
  (string-cat-reverse/aux
   (fold (lambda (s a) (+ (string-length s) a)) 0 string-list)
   string-list))

(define (string-cat-reverse/aux len string-list)
  (let ((res (make-string len)))
    (let lp ((i len) (ls string-list))
      (if (pair? ls)
          (let* ((s (car ls))
                 (slen (string-length s))
                 (i (- i slen)))
            (%%string-copy! res i s 0 slen)
            (lp i (cdr ls)))))
    res))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; List Utilities

;; like the one-arg IOTA case
(define (zero-to n)
  (if (<= n 0)
      '()
      (let lp ((i (- n 1)) (res '()))
        (if (zero? i) (cons 0 res) (lp (- i 1) (cons i res))))))

;; SRFI-1 extracts (simplified 1-ary versions)

(define (find pred ls)
  (cond ((find-tail pred ls) => car)
        (else #f)))

(define (find-tail pred ls)
  (let lp ((ls ls))
    (cond ((null? ls) #f)
          ((pred (car ls)) ls)
          (else (lp (cdr ls))))))

(define (last ls)
  (if (not (pair? ls))
      (error "can't take last of empty list" ls)
      (let lp ((ls ls))
        (if (pair? (cdr ls))
            (lp (cdr ls))
            (car ls)))))

(define (any pred ls)
  (and (pair? ls)
       (let lp ((head (car ls)) (tail (cdr ls)))
         (if (null? tail)
             (pred head)
             (or (pred head) (lp (car tail) (cdr tail)))))))

(define (every pred ls)
  (or (null? ls)
      (let lp ((head (car ls))  (tail (cdr ls)))
        (if (null? tail)
            (pred head)
            (and (pred head) (lp (car tail) (cdr tail)))))))

(define (fold kons knil ls)
  (let lp ((ls ls) (res knil))
    (if (null? ls)
        res
        (lp (cdr ls) (kons (car ls) res)))))

(define (filter pred ls)
  (let lp ((ls ls) (res '()))
    (if (null? ls)
        (reverse res)
        (lp (cdr ls) (if (pred (car ls)) (cons (car ls) res) res)))))

(define (remove pred ls)
  (let lp ((ls ls) (res '()))
    (if (null? ls)
        (reverse res)
        (lp (cdr ls) (if (pred (car ls)) res (cons (car ls) res))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Flags

(define (bit-shr n i)
  (quotient n (expt 2 i)))

(define (bit-shl n i)
  (* n (expt 2 i)))

(define (bit-not n) (- #xFFFF n))

(define (bit-ior a b)
  (cond
   ((zero? a) b)
   ((zero? b) a)
   (else
    (+ (if (or (odd? a) (odd? b)) 1 0)
       (* 2 (bit-ior (quotient a 2) (quotient b 2)))))))

(define (bit-and a b)
  (cond
   ((zero? a) 0)
   ((zero? b) 0)
   (else
    (+ (if (and (odd? a) (odd? b)) 1 0)
       (* 2 (bit-and (quotient a 2) (quotient b 2)))))))

(define (integer-log n)
  (define (b8 n r)
    (if (>= n (bit-shl 1 8)) (b4 (bit-shr n 8) (+ r 8)) (b4 n r)))
  (define (b4 n r)
    (if (>= n (bit-shl 1 4)) (b2 (bit-shr n 4) (+ r 4)) (b2 n r)))
  (define (b2 n r)
    (if (>= n (bit-shl 1 2)) (b1 (bit-shr n 2) (+ r 2)) (b1 n r)))
  (define (b1 n r) (if (>= n (bit-shl 1 1)) (+ r 1) r))
  (if (>= n (bit-shl 1 16)) (b8 (bit-shr n 16) 16) (b8 n 0)))

(define (flag-set? flags i)
  (= i (bit-and flags i)))
(define (flag-join a b)
  (if b (bit-ior a b) a))
(define (flag-clear a b)
  (bit-and a (bit-not b)))

(define ~none 0)
(define ~searcher? 1)
(define ~consumer? 2)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Parsing Embedded SREs in PCRE Strings

;; (define (with-read-from-string str i proc)
;;   (define (port-size in)
;;     (let lp ((i 0)) (if (eof-object? (read-char in)) i (lp (+ i 1)))))
;;   (let* ((len (string-length str))
;;          (tail-len (- len i))
;;          (in (open-input-string (substring str i len)))
;;          (sre (read in))
;;          (unused-len (port-size in)))
;;     (close-input-port in)
;;     (proc sre (- tail-len unused-len))))

(define close-token (list 'close))
(define dot-token (string->symbol "."))

(define (with-read-from-string str i proc)
  (define end (string-length str))
  (define (read i k)
    (cond
     ((>= i end) (error "unterminated embedded SRE" str))
     (else
      (case (string-ref str i)
        ((#\()
         (let lp ((i (+ i 1)) (ls '()))
           (read
            i
            (lambda (x j)
              (cond
               ((eq? x close-token)
                (k (reverse ls) j))
               ((eq? x dot-token)
                (if (null? ls)
                    (error "bad dotted form" str)
                    (read j (lambda (y j2)
                              (read j2 (lambda (z j3)
                                         (if (not (eq? z close-token))
                                             (error "bad dotted form" str)
                                             (k (append (reverse (cdr ls))
                                                        (cons (car ls) y))
                                                j3))))))))
               (else
                (lp j (cons x ls))))))))
        ((#\))
         (k close-token (+ i 1)))
        ((#\;)
         (let skip ((i (+ i 1)))
           (if (or (>= i end) (eqv? #\newline (string-ref str i)))
               (read (+ i 1) k)
               (skip (+ i 1)))))
        ((#\' #\`)
         (read (+ i 1)
           (lambda (sexp j)
             (let ((q (if (eqv? #\' (string-ref str i)) 'quote 'quasiquote)))
               (k (list q sexp) j)))))
        ((#\,)
         (let* ((at? (and (< (+ i 1) end) (eqv? #\@ (string-ref str (+ i 1)))))
                (u (if at? 'uquote-splicing 'unquote))
                (j (if at? (+ i 2) (+ i 1))))
           (read j (lambda (sexp j) (k (list u sexp) j)))))
        ((#\")
         (let scan ((from (+ i 1)) (i (+ i 1)) (res '()))
           (define (collect)
             (if (= from i) res (cons (substring str from i) res)))
           (if (>= i end)
               (error "unterminated string in embedded SRE" str)
               (case (string-ref str i)
                 ((#\") (k (string-cat-reverse (collect)) (+ i 1)))
                 ((#\\) (scan (+ i 1) (+ i 2) (collect)))
                 (else (scan from (+ i 1) res))))))
        ((#\#)
         (case (string-ref str (+ i 1))
           ((#\;)
            (read (+ i 2) (lambda (sexp j) (read j k))))
           ((#\\)
            (read (+ i 2)
              (lambda (sexp j)
                (k (case sexp
                     ((space) #\space)
                     ((newline) #\newline)
                     (else (let ((s (if (number? sexp)
                                        (number->string sexp)
                                        (symbol->string sexp))))
                             (string-ref s 0))))
                   j))))
           ((#\t #\f)
            (k (eqv? #\t (string-ref str (+ i 1))) (+ i 2)))
           (else
            (error "bad # syntax in simplified SRE" i))))
        (else
         (cond
          ((char-whitespace? (string-ref str i))
           (read (+ i 1) k))
          (else ;; symbol/number
           (let scan ((j (+ i 1)))
             (cond
              ((or (>= j end)
                   (let ((c (string-ref str j)))
                     (or (char-whitespace? c)
                         (memv c '(#\; #\( #\) #\" #\# #\\)))))
               (let ((str2 (substring str i j)))
                 (k (or (string->number str2) (string->symbol str2)) j)))
              (else (scan (+ j 1))))))))))))
  (read i (lambda (res j)
            (if (eq? res 'close-token)
                (error "unexpected ')' in SRE" str j)
                (proc res j)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Parsing PCRE Strings

(define ~save? 1)
(define ~case-insensitive? 2)
(define ~multi-line? 4)
(define ~single-line? 8)
(define ~ignore-space? 16)
(define ~utf8? 32)

(define (symbol-list->flags ls)
  (let lp ((ls ls) (res ~none))
    (if (not (pair? ls))
        res
        (lp (cdr ls)
            (flag-join
             res
             (case (car ls)
               ((i ci case-insensitive) ~case-insensitive?)
               ((m multi-line) ~multi-line?)
               ((s single-line) ~single-line?)
               ((x ignore-space) ~ignore-space?)
               ((u utf8) (if *allow-utf8-mode?* ~utf8? ~none))
               (else #f)))))))

(define (maybe-string->sre obj)
  (if (string? obj) (string->sre obj) obj))

(define (string->sre str . o)
  (if (not (string? str)) (error "string->sre: expected a string" str))
  (let ((end (string-length str))
        (flags (symbol-list->flags o)))

    (let lp ((i 0) (from 0) (flags flags) (res '()) (st '()))

      ;; handle case sensitivity at the literal char/string level
      (define (cased-char ch)
        (if (and (flag-set? flags ~case-insensitive?)
                 (char-alphabetic? ch))
            `(or ,ch ,(char-altcase ch))
            ch))
      (define (cased-string str)
        (if (flag-set? flags ~case-insensitive?)
            (sre-sequence (map cased-char (string->list str)))
            str))
      ;; accumulate the substring from..i as literal text
      (define (collect)
        (if (= i from) res (cons (cased-string (substring str from i)) res)))
      ;; like collect but breaks off the last single character when
      ;; collecting literal data, as the argument to ?/*/+ etc.
      (define (collect/single)
        (let* ((utf8? (flag-set? flags ~utf8?))
               (j (if (and utf8? (> i 1))
                      (utf8-backup-to-initial-char str (- i 1))
                      (- i 1))))
          (cond
           ((< j from)
            res)
           (else
            (let ((c (cased-char (if utf8?
                                     (utf8-string-ref str j (- i j))
                                     (string-ref str j)))))
              (cond
               ((= j from)
                (cons c res))
               (else
                (cons c
                      (cons (cased-string (substring str from j))
                            res)))))))))
      ;; collects for use as a result, reversing and grouping OR
      ;; terms, and some ugly tweaking of `function-like' groups and
      ;; conditionals
      (define (collect/terms)
        (let* ((ls (collect))
               (func
                (and (pair? ls)
                     (memq (last ls)
                           '(atomic if look-ahead neg-look-ahead
                                    look-behind neg-look-behind
                                    => submatch-named
                                    w/utf8 w/noutf8))))
               (prefix (if (and func (memq (car func) '(=> submatch-named)))
                           (list 'submatch-named (cadr (reverse ls)))
                           (and func (list (car func)))))
               (ls (if func
                       (if (memq (car func) '(=> submatch-named))
                           (reverse (cddr (reverse ls)))
                           (reverse (cdr (reverse ls))))
                       ls)))
          (let lp ((ls ls) (term '()) (res '()))
            (define (shift)
              (cons (sre-sequence term) res))
            (cond
             ((null? ls)
              (let* ((res (sre-alternate (shift)))
                     (res (if (flag-set? flags ~save?)
                              (list 'submatch res)
                              res)))
                (if prefix
                    (if (eq? 'if (car prefix))
                        (cond
                         ((not (pair? res))
                          'epsilon)
                         ((memq (car res)
                                '(look-ahead neg-look-ahead
                                             look-behind neg-look-behind))
                          res)
                         ((eq? 'seq (car res))
                          `(if ,(cadr res)
                               ,(sre-sequence (cddr res))))
                         (else
                          `(if ,(cadadr res)
                               ,(sre-sequence (cddadr res))
                               ,(sre-alternate (cddr res)))))
                        `(,@prefix ,res))
                    res)))
             ((eq? 'or (car ls)) (lp (cdr ls) '() (shift)))
             (else (lp (cdr ls) (cons (car ls) term) res))))))
      (define (save)
        (cons (cons flags (collect)) st))

      ;; main parsing
      (if (>= i end)
          (if (pair? st)
              (error "unterminated parenthesis in regexp" str)
              (collect/terms))
          (let ((c (string-ref str i)))
            (case c
              ((#\.)
               (lp (+ i 1) (+ i 1) flags
                   (cons (if (flag-set? flags ~single-line?) 'any 'nonl)
                         (collect))
                   st))
              ((#\?)
               (let ((res (collect/single)))
                 (if (null? res)
                     (error "? can't follow empty pattern" str res)
                     (let ((x (car res)))
                       (lp (+ i 1)
                           (+ i 1)
                           flags
                           (cons
                            (if (pair? x)
                                (case (car x)
                                  ((*)  `(*? ,@(cdr x)))
                                  ((+)  `(**? 1 #f ,@(cdr x)))
                                  ((?)  `(?? ,@(cdr x)))
                                  ((**) `(**? ,@(cdr x)))
                                  ((=)  `(**? ,(cadr x) ,@(cdr x)))
                                  ((>=)  `(**? ,(cadr x) #f ,@(cddr x)))
                                  (else `(? ,x)))
                                `(? ,x))
                            (cdr res))
                           st)))))
              ((#\+ #\*)
               (let* ((res (collect/single))
                      (x (if (pair? res) (car res) 'epsilon))
                      (op (string->symbol (string c))))
                 (cond
                  ((sre-repeater? x)
                   (error "duplicate repetition (e.g. **) in pattern" str res))
                  ((sre-empty? x)
                   (error "can't repeat empty pattern (e.g. ()*)" str res))
                  (else
                   (lp (+ i 1) (+ i 1) flags
                       (cons (list op x) (cdr res))
                       st)))))
              ((#\()
               (cond
                ((>= (+ i 1) end)
                 (error "unterminated parenthesis in regexp" str))
                ((not (memv (string-ref str (+ i 1)) '(#\? #\*))) ; normal case
                 (lp (+ i 1) (+ i 1) (flag-join flags ~save?) '() (save)))
                ((>= (+ i 2) end)
                 (error "unterminated parenthesis in regexp" str))
                ((eqv? (string-ref str (+ i 1)) #\*)
                 (if (eqv? #\' (string-ref str (+ i 2)))
                     (with-read-from-string str (+ i 3)
                       (lambda (sre j)
                         (if (or (>= j end) (not (eqv? #\) (string-ref str j))))
                             (error "unterminated (*'...) SRE escape" str)
                             (lp (+ j 1) (+ j 1) flags (cons sre (collect)) st))))
                     (error "bad regexp syntax: (*FOO) not supported" str)))
                (else                   ;; (?...) case
                 (case (string-ref str (+ i 2))
                   ((#\#)
                    (let ((j (string-scan-char str #\) (+ i 3))))
                      (if (not j)
                          (error "missing ) after #" str)
                          (lp (+ j i) (+ j 1) flags (collect) st))))
                   ((#\:)
                    (lp (+ i 3) (+ i 3) (flag-clear flags ~save?) '() (save)))
                   ((#\=)
                    (lp (+ i 3) (+ i 3) (flag-clear flags ~save?)
                        '(look-ahead) (save)))
                   ((#\!)
                    (lp (+ i 3) (+ i 3) (flag-clear flags ~save?)
                        '(neg-look-ahead) (save)))
                   ((#\<)
                    (cond
                     ((>= (+ i 3) end)
                      (error "unterminated parenthesis in regexp" str))
                     (else
                      (case (string-ref str (+ i 3))
                        ((#\=)
                         (lp (+ i 4) (+ i 4) (flag-clear flags ~save?)
                             '(look-behind) (save)))
                        ((#\!)
                         (lp (+ i 4) (+ i 4) (flag-clear flags ~save?)
                             '(neg-look-behind) (save)))
                        (else
                         (let ((j (and (char-alphabetic?
                                        (string-ref str (+ i 3)))
                                       (string-scan-char str #\> (+ i 4)))))
                           (if j
                               (lp (+ j 1) (+ j 1) (flag-clear flags ~save?)
                                   `(,(string->symbol (substring str (+ i 3) j))
                                     submatch-named)
                                   (save))
                               (error "invalid (?< sequence" str))))))))
                   ((#\>)
                    (lp (+ i 3) (+ i 3) (flag-clear flags ~save?)
                        '(atomic) (save)))
                   ;;((#\' #\P) ; named subpatterns
                   ;; )
                   ;;((#\R) ; recursion
                   ;; )
                   ((#\()
                    (cond
                     ((>= (+ i 3) end)
                      (error "unterminated parenthesis in regexp" str))
                     ((char-numeric? (string-ref str (+ i 3)))
                      (let ((j (string-scan-char str #\) (+ i 3))))
                        (if (not j)
                            (error "missing closing parenthesis" str i)
                            (let ((n (string->number (substring str (+ i 3) j))))
                              (if (not n)
                                  (error "invalid conditional reference" str)
                                  (lp (+ j 1) (+ j 1) (flag-clear flags ~save?)
                                      `(,n if) (save)))))))
                     ((char-alphabetic? (string-ref str (+ i 3)))
                      (let ((j (string-scan-char str #\) (+ i 3))))
                        (if (not j)
                            (error "missing closing parenthesis" str i)
                            (let ((s (string->symbol (substring str (+ i 3) j))))
                              (lp (+ j 1) (+ j 1) (flag-clear flags ~save?)
                                  `(,s if) (save))))))
                     (else
                      (lp (+ i 2) (+ i 2) (flag-clear flags ~save?)
                          '(if) (save)))))
                   ((#\{)
                    (error "unsupported Perl-style cluster" str))
                   (else
                    (let ((old-flags flags))
                      (let lp2 ((j (+ i 2)) (flags flags) (invert? #f))
                        (define (join x)
                          ((if invert? flag-clear flag-join) flags x))
                        (define (new-res res)
                          (let ((before (flag-set? old-flags ~utf8?))
                                (after (flag-set? flags ~utf8?)))
                            (if (eq? before after)
                                res
                                (cons (if after 'w/utf8 'w/noutf8) res))))
                        (cond
                         ((>= j end)
                          (error "incomplete cluster" str i))
                         (else
                          (case (string-ref str j)
                            ((#\i)
                             (lp2 (+ j 1) (join ~case-insensitive?) invert?))
                            ((#\m)
                             (lp2 (+ j 1) (join ~multi-line?) invert?))
                            ((#\x)
                             (lp2 (+ j 1) (join ~ignore-space?) invert?))
                            ((#\u)
                             (if *allow-utf8-mode?*
                                 (lp2 (+ j 1) (join ~utf8?) invert?)
                                 (lp2 (+ j 1) flags invert?)))
                            ((#\-)
                             (lp2 (+ j 1) flags (not invert?)))
                            ((#\))
                             (lp (+ j 1) (+ j 1) flags (new-res (collect))
                                 st))
                            ((#\:)
                             (lp (+ j 1) (+ j 1) flags (new-res '())
                                 (cons (cons old-flags (collect)) st)))
                            (else
                             (error "unknown regex cluster modifier" str)
                             )))))))))))
              ((#\))
               (if (null? st)
                   (error "too many )'s in regexp" str)
                   (lp (+ i 1)
                       (+ i 1)
                       (caar st)
                       (cons (collect/terms) (cdar st))
                       (cdr st))))
              ((#\[)
               (apply
                (lambda (sre j)
                  (lp (+ j 1) (+ j 1) flags (cons sre (collect)) st))
                (string-parse-cset str (+ i 1) flags)))
              ((#\{)
               (cond
                ((or (>= (+ i 1) end)
                     (not (or (char-numeric? (string-ref str (+ i 1)))
                              (eqv? #\, (string-ref str (+ i 1))))))
                 (lp (+ i 1) from flags res st))
                (else
                 (let ((res (collect/single)))
                   (cond
                    ((null? res)
                     (error "{ can't follow empty pattern"))
                    (else
                     (let* ((x (car res))
                            (tail (cdr res))
                            (j (or (string-scan-char str #\} (+ i 1))
                                   (error "missing closing }" str i)))
                            (s2 (string-split-char (substring str (+ i 1) j)
                                                   #\,))
                            (n (string->number (car s2)))
                            (m (and (pair? (cdr s2))
                                    (string->number (cadr s2)))))
                       (cond
                        ((or (not n)
                             (and (pair? (cdr s2))
                                  (not (equal? "" (cadr s2)))
                                  (not m)))
                         (error "invalid {n} repetition syntax" s2))
                        ((null? (cdr s2))
                         (lp (+ j 1) (+ j 1) flags `((= ,n ,x) ,@tail) st))
                        (m
                         (lp (+ j 1) (+ j 1) flags `((** ,n ,m ,x) ,@tail) st))
                        (else
                         (lp (+ j 1) (+ j 1) flags `((>= ,n ,x) ,@tail) st)
                         )))))))))
              ((#\\)
               (cond
                ((>= (+ i 1) end)
                 (error "incomplete escape sequence" str))
                (else
                 (let ((c (string-ref str (+ i 1))))
                   (case c
                     ((#\d)
                      (lp (+ i 2) (+ i 2) flags `(numeric ,@(collect)) st))
                     ((#\D)
                      (lp (+ i 2) (+ i 2) flags `((~ numeric) ,@(collect)) st))
                     ((#\s)
                      (lp (+ i 2) (+ i 2) flags `(space ,@(collect)) st))
                     ((#\S)
                      (lp (+ i 2) (+ i 2) flags `((~ space) ,@(collect)) st))
                     ((#\w)
                      (lp (+ i 2) (+ i 2) flags
                          `((or alphanumeric ("_")) ,@(collect)) st))
                     ((#\W)
                      (lp (+ i 2) (+ i 2) flags
                          `((~ (or alphanumeric ("_"))) ,@(collect)) st))
                     ((#\b)
                      (lp (+ i 2) (+ i 2) flags
                          `((or bow eow) ,@(collect)) st))
                     ((#\B)
                      (lp (+ i 2) (+ i 2) flags `(nwb ,@(collect)) st))
                     ((#\A)
                      (lp (+ i 2) (+ i 2) flags `(bos ,@(collect)) st))
                     ((#\Z)
                      (lp (+ i 2) (+ i 2) flags
                          `((? #\newline) eos ,@(collect)) st))
                     ((#\z)
                      (lp (+ i 2) (+ i 2) flags `(eos ,@(collect)) st))
                     ((#\R)
                      (lp (+ i 2) (+ i 2) flags `(newline ,@(collect)) st))
                     ((#\K)
                      (lp (+ i 2) (+ i 2) flags `(reset ,@(collect)) st))
                     ;; these two are from Emacs and TRE, but not in PCRE
                     ((#\<)
                      (lp (+ i 2) (+ i 2) flags `(bow ,@(collect)) st))
                     ((#\>)
                      (lp (+ i 2) (+ i 2) flags `(eow ,@(collect)) st))
                     ((#\x)
                      (apply
                       (lambda (ch j)
                         (lp (+ j 1) (+ j 1) flags `(,ch ,@(collect)) st))
                       (string-parse-hex-escape str (+ i 2) end)))
                     ((#\k)
                      (let ((c (string-ref str (+ i 2))))
                        (if (not (memv c '(#\< #\{ #\')))
                            (error "bad \\k usage, expected \\k<...>" str)
                            (let* ((terminal (char-mirror c))
                                   (j (string-scan-char str terminal (+ i 2)))
                                   (s (and j (substring str (+ i 3) j)))
                                   (backref
                                    (if (flag-set? flags ~case-insensitive?)
                                        'backref-ci
                                        'backref)))
                              (if (not j)
                                  (error "unterminated named backref" str)
                                  (lp (+ j 1) (+ j 1) flags
                                      `((,backref ,(string->symbol s))
                                        ,@(collect))
                                      st))))))
                     ((#\Q)  ;; \Q..\E escapes
                      (let ((res (collect)))
                        (let lp2 ((j (+ i 2)))
                          (cond
                           ((>= j end)
                            (lp j (+ i 2) flags res st))
                           ((eqv? #\\ (string-ref str j))
                            (cond
                             ((>= (+ j 1) end)
                              (lp (+ j 1) (+ i 2) flags res st))
                             ((eqv? #\E (string-ref str (+ j 1)))
                              (lp (+ j 2) (+ j 2) flags
                                  (cons (substring str (+ i 2) j) res) st))
                             (else
                              (lp2 (+ j 2)))))
                           (else
                            (lp2 (+ j 1)))))))
                     ((#\')
                      (with-read-from-string str (+ i 2)
                       (lambda (sre j)
                         (lp j j flags (cons sre (collect)) st))))
                     ;;((#\p)  ; XXXX unicode properties
                     ;; )
                     ;;((#\P)
                     ;; )
                     (else
                      (cond
                       ((char-numeric? c)
                        (let* ((j (or (string-scan-pred
                                       str
                                       (lambda (c) (not (char-numeric? c)))
                                       (+ i 2))
                                      end))
                               (backref
                                (if (flag-set? flags ~case-insensitive?)
                                    'backref-ci
                                    'backref))
                               (res `((,backref ,(string->number
                                                  (substring str (+ i 1) j)))
                                      ,@(collect))))
                          (lp j j flags res st)))
                       ((char-alphabetic? c)
                        (let ((cell (assv c posix-escape-sequences)))
                          (if cell
                              (lp (+ i 2) (+ i 2) flags
                                  (cons (cdr cell) (collect)) st)
                              (error "unknown escape sequence" str c))))
                       (else
                        (lp (+ i 2) (+ i 1) flags (collect) st)))))))))
              ((#\|)
               (lp (+ i 1) (+ i 1) flags (cons 'or (collect)) st))
              ((#\^)
               (let ((sym (if (flag-set? flags ~multi-line?) 'bol 'bos)))
                 (lp (+ i 1) (+ i 1) flags (cons sym (collect)) st)))
              ((#\$)
               (let ((sym (if (flag-set? flags ~multi-line?) 'eol 'eos)))
                 (lp (+ i 1) (+ i 1) flags (cons sym (collect)) st)))
              ((#\space)
               (if (flag-set? flags ~ignore-space?)
                   (lp (+ i 1) (+ i 1) flags (collect) st)
                   (lp (+ i 1) from flags res st)))
              ((#\#)
               (if (flag-set? flags ~ignore-space?)
                   (let ((j (or (string-scan-char str #\newline (+ i 1))
                                (- end 1))))
                     (lp (+ j 1) (+ j 1) flags (collect) st))
                   (lp (+ i 1) from flags res st)))
              (else
               (lp (+ i 1) from flags res st))))))))

(define posix-escape-sequences
  `((#\n . #\newline)
    (#\r . ,(integer->char (+ (char->integer #\newline) 3)))
    (#\t . ,(integer->char (- (char->integer #\newline) 1)))
    (#\a . ,(integer->char (- (char->integer #\newline) 3)))
    (#\e . ,(integer->char (+ (char->integer #\newline) #x11)))
    (#\f . ,(integer->char (+ (char->integer #\newline) 2)))
    ))

(define (char-altcase c)
  (if (char-upper-case? c) (char-downcase c) (char-upcase c)))

(define (char-mirror c)
  (case c ((#\<) #\>) ((#\{) #\}) ((#\() #\)) ((#\[) #\]) (else c)))

(define (string-parse-hex-escape str i end)
  (cond
   ((>= i end)
    (error "incomplete hex escape" str i))
   ((eqv? #\{ (string-ref str i))
    (let ((j (string-scan-char-escape str #\} (+ i 1))))
      (if (not j)
          (error "incomplete hex brace escape" str i)
          (let* ((s (substring str (+ i 1) j))
                 (n (string->number s 16)))
            (if n
                (list (integer->char n) j)
                (error "bad hex brace escape" s))))))
   ((>= (+ i 1) end)
    (error "incomplete hex escape" str i))
   (else
    (let* ((s (substring str i (+ i 2)))
           (n (string->number s 16)))
      (if n
          (list (integer->char n) (+ i 2))
          (error "bad hex escape" s))))))

(define (string-parse-cset str start flags)
  (let* ((end (string-length str))
         (invert? (and (< start end) (eqv? #\^ (string-ref str start))))
         (utf8? (flag-set? flags ~utf8?)))
    (define (go i prev-char cset)
      (if (>= i end)
          (error "incomplete char set" str i end)
          (let ((c (string-ref str i)))
            (case c
              ((#\])
               (if (cset-empty? cset)
                   (go (+ i 1) #\] (cset-adjoin cset #\]))
                   (let ((ci? (flag-set? flags ~case-insensitive?)))
                     (list
                      (let ((res (if ci? (cset-case-insensitive cset) cset)))
                        (cset->sre (if invert? (cset-complement res) res)))
                      i))))
              ((#\-)
               (cond
                ((or (= i start)
                     (and (= i (+ start 1)) (eqv? #\^ (string-ref str start)))
                     (eqv? #\] (string-ref str (+ i 1))))
                 (go (+ i 1) c (cset-adjoin cset c)))
                ((not prev-char)
                 (error "bad char-set"))
                (else
                 (let ((char (string-ref str (+ i 1))))
                   (apply
                    (lambda (c j)
                      (if (char<? c prev-char)
                          (error "inverted range in char-set" prev-char c)
                          (go j #f (cset-union cset (range->cset prev-char c)))))
                    (cond
                     ((and (eqv? #\\ char) (assv char posix-escape-sequences))
                      => (lambda (x) (list (cdr x) (+ i 3))))
                     ((and (eqv? #\\ char)
                           (eqv? (string-ref str (+ i 2)) #\x))
                      (string-parse-hex-escape str (+ i 3) end))
                     ((and utf8? (<= #x80 (char->integer char) #xFF))
                      (let ((len (utf8-start-char->length char)))
                        (list (utf8-string-ref str (+ i 1) len) (+ i 1 len))))
                     (else
                      (list char (+ i 2)))))))))
              ((#\[)
               (let* ((inv? (eqv? #\^ (string-ref str (+ i 1))))
                      (i2 (if inv? (+ i 2) (+ i 1))))
                 (case (string-ref str i2)
                   ((#\:)
                    (let ((j (string-scan-char str #\: (+ i2 1))))
                      (if (or (not j) (not (eqv? #\] (string-ref str (+ j 1)))))
                          (error "incomplete character class" str)
                          (let* ((class (sre->cset
                                         (string->symbol
                                          (substring str (+ i2 1) j))))
                                 (class (if inv? (cset-complement class) class)))
                            (go (+ j 2) #f (cset-union cset class))))))
                   ((#\= #\.)
                    (error "collating sequences not supported" str))
                   (else
                    (go (+ i 1) #\[ (cset-adjoin cset #\[))))))
              ((#\\)
               (let ((c (string-ref str (+ i 1))))
                 (case c
                   ((#\d #\D #\s #\S #\w #\W)
                    (go (+ i 2) #f
                        (cset-union cset
                                    (sre->cset (string->sre (string #\\ c))))))
                   ((#\x)
                    (apply
                     (lambda (ch j)
                       (go j ch (cset-adjoin cset ch)))
                     (string-parse-hex-escape str (+ i 2) end)))
                   (else
                    (let ((c (cond ((assv c posix-escape-sequences) => cdr)
                                   (else c))))
                      (go (+ i 2) c (cset-adjoin cset c)))))))
              (else
               (if (and utf8? (<= #x80 (char->integer c) #xFF))
                   (let ((len (utf8-start-char->length c)))
                     (go (+ i len)
                         (utf8-string-ref str i len)
                         (cset-adjoin cset (utf8-string-ref str i len))))
                   (go (+ i 1) c (cset-adjoin cset c))))))))
    (if invert?
        (go (+ start 1)
            #f
            (if (flag-set? flags ~multi-line?)
                (char->cset #\newline)
                (make-cset)))
        (go start #f (make-cset)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; UTF-8 Utilities

;; Here are some hairy optimizations that need to be documented
;; better.  Thanks to these, we never do any utf8 processing once the
;; regexp is compiled.

;; two chars: ab..ef
;;            a[b..xFF]|[b-d][x80..xFF]|e[x80..xFF]

;; three chars: abc..ghi
;;              ab[c..xFF]|a[d..xFF][x80..xFF]|
;;              [b..f][x80..xFF][x80..xFF]|
;;              g[x80..g][x80..xFF]|gh[x80..i]

;; four chars: abcd..ghij
;;             abc[d..xFF]|ab[d..xFF][x80..xFF]|a[c..xFF][x80..xFF][x80..xFF]|
;;             [b..f][x80..xFF][x80..xFF][x80..xFF]|
;;             g[x80..g][x80..xFF][x80..xFF]|gh[x80..h][x80..xFF]|ghi[x80..j]

(define (high-char? c) (<= #x80 (char->integer c)))

;; number of total bytes in a utf8 char given the 1st byte

(define utf8-start-char->length
  (let ((table '#(
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 0x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 1x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 2x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 3x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 4x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 5x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 6x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 7x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 8x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; 9x
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; ax
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ; bx
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 ; cx
2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 ; dx
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 ; ex
4 4 4 4 4 4 4 4 5 5 5 5 6 6 0 0 ; fx
)))
    (lambda (c) (vector-ref table (char->integer c)))))

(define (utf8-string-ref str i len)
  (define (byte n) (char->integer (string-ref str n)))
  (case len
    ((1) ; shouldn't happen in this module
     (string-ref str i))
    ((2)
     (integer->char
      (+ (bit-shl (bit-and (byte i) #b00011111) 6)
         (bit-and (byte (+ i 1)) #b00111111))))
    ((3)
     (integer->char
      (+ (bit-shl (bit-and (byte i) #b00001111) 12)
         (bit-shl (bit-and (byte (+ i 1)) #b00111111) 6)
         (bit-and (byte (+ i 2)) #b00111111))))
    ((4)
     (integer->char
      (+ (bit-shl (bit-and (byte i) #b00000111) 18)
         (bit-shl (bit-and (byte (+ i 1)) #b00111111) 12)
         (bit-shl (bit-and (byte (+ i 2)) #b00111111) 6)
         (bit-and (byte (+ i 3)) #b00111111))))
    (else
     (error "invalid utf8 length" str len i))))

(define (utf8-backup-to-initial-char str i)
  (let lp ((i i))
    (if (= i 0)
        0
        (let ((c (char->integer (string-ref str i))))
          (if (or (< c #x80) (>= c #xC0))
              i
              (lp (- i 1)))))))

(define (utf8-lowest-digit-of-length len)
  (case len
    ((1) 0) ((2) #xC0) ((3) #xE0) ((4) #xF0)
    (else (error "invalid utf8 length" len))))

(define (utf8-highest-digit-of-length len)
  (case len
    ((1) #x7F) ((2) #xDF) ((3) #xEF) ((4) #xF7)
    (else (error "invalid utf8 length" len))))

(define (char->utf8-list c)
  (let ((i (char->integer c)))
    (cond
     ((<= i #x7F) (list i))
     ((<= i #x7FF)
      (list (bit-ior #b11000000 (bit-shr i 6))
            (bit-ior #b10000000 (bit-and i #b111111))))
     ((<= i #xFFFF)
      (list (bit-ior #b11100000 (bit-shr i 12))
            (bit-ior #b10000000 (bit-and (bit-shr i 6) #b111111))
            (bit-ior #b10000000 (bit-and i #b111111))))
     ((<= i #x1FFFFF)
      (list (bit-ior #b11110000 (bit-shr i 18))
            (bit-ior #b10000000 (bit-and (bit-shr i 12) #b111111))
            (bit-ior #b10000000 (bit-and (bit-shr i 6) #b111111))
            (bit-ior #b10000000 (bit-and i #b111111))))
     (else (error "unicode codepoint out of range:" i)))))

(define (unicode-range->utf8-pattern lo hi)
  (let ((lo-ls (char->utf8-list lo))
        (hi-ls (char->utf8-list hi)))
    (if (not (= (length lo-ls) (length hi-ls)))
        (sre-alternate (list (unicode-range-climb-digits lo-ls hi-ls)
                             (unicode-range-up-to hi-ls)))
        (let lp ((lo-ls lo-ls) (hi-ls hi-ls))
          (cond
           ((= (car lo-ls) (car hi-ls))
            (sre-sequence
              (cons (integer->char (car lo-ls))
                (if (null? (cdr lo-ls)) '()
                    (cons (lp (cdr lo-ls) (cdr hi-ls)) '())))))
           ((= (+ (car lo-ls) 1) (car hi-ls))
            (sre-alternate (list (unicode-range-up-from lo-ls)
                                 (unicode-range-up-to hi-ls))))
           (else
            (sre-alternate (list (unicode-range-up-from lo-ls)
                                 (unicode-range-middle lo-ls hi-ls)
                                 (unicode-range-up-to hi-ls)))))))))

(define (unicode-range-helper one ls prefix res)
  (if (null? ls)
      res
      (unicode-range-helper
       one
       (cdr ls)
       (cons (car ls) prefix)
       (cons (sre-sequence
              `(,@(map integer->char prefix)
                ,(one (car ls))
                ,@(map (lambda (_)
                         `(/ ,(integer->char #x80)
                             ,(integer->char #xFF)))
                       (cdr ls))))
             res))))

(define (unicode-range-up-from lo-ls)
  (sre-sequence
   (list (integer->char (car lo-ls))
         (sre-alternate
          (unicode-range-helper
           (lambda (c)
             `(/ ,(integer->char (+ (car lo-ls) 1)) ,(integer->char #xFF)))
           (cdr (reverse (cdr lo-ls)))
           '()
           (list
            (sre-sequence
             (append
              (map integer->char (reverse (cdr (reverse (cdr lo-ls)))))
              `((/ ,(integer->char (last lo-ls))
                   ,(integer->char #xFF)))))))))))

(define (unicode-range-up-to hi-ls)
  (sre-sequence
   (list (integer->char (car hi-ls))
         (sre-alternate
          (unicode-range-helper
           (lambda (c)
             `(/ ,(integer->char #x80) ,(integer->char (- (car hi-ls) 1))))
           (cdr (reverse (cdr hi-ls)))
           '()
           (list
            (sre-sequence
             (append
              (map integer->char (reverse (cdr (reverse (cdr hi-ls)))))
              `((/ ,(integer->char #x80)
                   ,(integer->char (last hi-ls))))))))))))

(define (unicode-range-climb-digits lo-ls hi-ls)
  (let ((lo-len (length lo-ls)))
    (sre-alternate
     (append
      (list
       (sre-sequence
        (cons `(/ ,(integer->char (car lo-ls))
                  ,(integer->char (if (<= (car lo-ls) #x7F) #x7F #xFF)))
              (map (lambda (_)
                     `(/ ,(integer->char #x80) ,(integer->char #xFF)))
                   (cdr lo-ls)))))
      (map
       (lambda (i)
         (sre-sequence
          (cons
           `(/ ,(integer->char (utf8-lowest-digit-of-length (+ i lo-len 1)))
               ,(integer->char (utf8-highest-digit-of-length (+ i lo-len 1))))
           (map (lambda (_)
                  `(/ ,(integer->char #x80) ,(integer->char #xFF)))
                (zero-to (+ i lo-len))))))
       (zero-to (- (length hi-ls) (+ lo-len 1))))
      (list
       (sre-sequence
        (cons `(/ ,(integer->char
                    (utf8-lowest-digit-of-length
                     (utf8-start-char->length
                      (integer->char (- (car hi-ls) 1)))))
                  ,(integer->char (- (car hi-ls) 1)))
              (map (lambda (_)
                     `(/ ,(integer->char #x80) ,(integer->char #xFF)))
                   (cdr hi-ls)))))))))

(define (unicode-range-middle lo-ls hi-ls)
  (let ((lo (integer->char (+ (car lo-ls) 1)))
        (hi (integer->char (- (car hi-ls) 1))))
    (sre-sequence
     (cons (if (char=? lo hi) lo `(/ ,lo ,hi))
           (map (lambda (_) `(/ ,(integer->char #x80) ,(integer->char #xFF)))
                (cdr lo-ls))))))

;; Maybe this should just modify the input?
(define (cset->utf8-pattern cset)
  (let lp ((ls (cset->plist cset)) (alts '()) (lo-cset '()))
    (if (null? ls)
        (sre-alternate (append (reverse alts)
                               (if (null? lo-cset)
                                   '()
                                   (list (cons '/ (reverse lo-cset))))))
        (if (or (high-char? (car ls))  (high-char? (cadr ls)))
            (lp (cddr ls)
                (cons (unicode-range->utf8-pattern (car ls) (cadr ls)) alts)
                lo-cset)
            (lp (cddr ls) alts (cons (cadr ls) (cons (car ls) lo-cset)))))))

(define (sre-adjust-utf8 sre flags)
  (let adjust ((sre sre)
               (utf8? (flag-set? flags ~utf8?))
               (ci? (flag-set? flags ~case-insensitive?)))
    (define (rec sre) (adjust sre utf8? ci?))
    (cond
     ((pair? sre)
      (case (car sre)
        ((w/utf8) (adjust (sre-sequence (cdr sre)) #t ci?))
        ((w/noutf8) (adjust (sre-sequence (cdr sre)) #f ci?))
        ((w/case)
         (cons (car sre) (map (lambda (s) (adjust s utf8? #f)) (cdr sre))))
        ((w/nocase)
         (cons (car sre) (map (lambda (s) (adjust s utf8? #t)) (cdr sre))))
        ((/ ~ & -)
         (if (not utf8?)
             sre
             (let ((cset (sre->cset sre ci?)))
               (if (any high-char? (cset->plist cset))
                   (if ci?
                       (list 'w/case (cset->utf8-pattern cset))
                       (cset->utf8-pattern cset))
                   sre))))
        ((*)
         (case (sre-sequence (cdr sre))
           ;; special case optimization: .* w/utf8 == .* w/noutf8
           ((any) '(* any))
           ((nonl) '(* nonl))
           (else (cons '* (map rec (cdr sre))))))
        (else
         (cons (car sre) (map rec (cdr sre))))))
     (else
      (case sre
        ((any) (if utf8? 'utf8-any 'any))
        ((nonl) (if utf8? 'utf8-nonl 'nonl))
        (else
         (if (and utf8? (char? sre) (high-char? sre))
             (sre-sequence (map integer->char (char->utf8-list sre)))
             sre)))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Compilation

(define (irregex x . o)
  (cond
   ((irregex? x) x)
   ((string? x) (apply string->irregex x o))
   (else (apply sre->irregex x o))))

(define (string->irregex str . o)
  (apply sre->irregex (apply string->sre str o) o))

(define (sre->irregex sre . o)
  (let* ((pat-flags (symbol-list->flags o))
         (sre (if *allow-utf8-mode?*
                  (sre-adjust-utf8 sre pat-flags)
                  sre))
         (searcher? (sre-searcher? sre))
         (sre-dfa (if searcher? (sre-remove-initial-bos sre) sre))
         (dfa-limit (cond ((memq 'small o) 1) ((memq 'fast o) 50) (else 10)))
         ;; TODO: Maybe make these two promises; if we only want to search,
         ;; it's wasteful to compile the matcher, and vice versa
         ;; Maybe provide a flag to compile eagerly, to help benchmarking etc.
         (dfa/search
          (cond ((memq 'backtrack o) #f)
                (searcher? #t)
                ((sre->nfa `(seq (* any) ,sre-dfa) pat-flags)
                 => (lambda (nfa)
                      (nfa->dfa nfa (* dfa-limit (nfa-num-states nfa)))))
                (else #f)))
         (dfa (cond ((and dfa/search (sre->nfa sre-dfa pat-flags))
                     => (lambda (nfa)
                          (nfa->dfa nfa (* dfa-limit (nfa-num-states nfa)))))
                    (else #f)))
         (submatches (sre-count-submatches sre-dfa))
         (names (sre-names sre-dfa 1 '()))
         (lens (sre-length-ranges sre-dfa names))
         (flags (flag-join
                 (flag-join ~none (and searcher? ~searcher?))
                 (and (sre-consumer? sre) ~consumer?))))
    (cond
     (dfa
      (make-irregex dfa dfa/search #f flags submatches lens names))
     (else
      (let ((f (sre->procedure sre pat-flags names)))
        (make-irregex #f #f f flags submatches lens names))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; SRE Analysis

;; returns #t if the sre can ever be empty
(define (sre-empty? sre)
  (if (pair? sre)
      (case (car sre)
        ((* ? look-ahead look-behind neg-look-ahead neg-look-behind) #t)
        ((**) (or (not (number? (cadr sre))) (zero? (cadr sre))))
        ((or) (any sre-empty? (cdr sre)))
        ((: seq $ submatch => submatch-named + atomic)
         (every sre-empty? (cdr sre)))
        (else #f))
      (memq sre '(epsilon bos eos bol eol bow eow commit))))

(define (sre-any? sre)
  (or (eq? sre 'any)
      (and (pair? sre)
           (case (car sre)
             ((seq : $ submatch => submatch-named)
              (and (pair? (cdr sre)) (null? (cddr sre)) (sre-any? (cadr sre))))
             ((or) (every sre-any? (cdr sre)))
             (else #f)))))

(define (sre-repeater? sre)
  (and (pair? sre)
       (or (memq (car sre) '(* +))
           (and (memq (car sre) '($ submatch => submatch-named seq :))
                (pair? (cdr sre))
                (null? (cddr sre))
                (sre-repeater? (cadr sre))))))

(define (sre-bos? sre)
  (if (pair? sre)
      (case (car sre)
        ((seq : $ submatch => submatch-named)
         (and (pair? (cdr sre)) (sre-bos? (cadr sre))))
        ((or) (every sre-bos? (cdr sre)))
        (else #f))
      (eq? 'bos sre)))

;; a searcher doesn't need explicit iteration to find the first match
(define (sre-searcher? sre)
  (or (sre-bos? sre)
      (and (pair? sre)
           (case (car sre)
             ((* +) (sre-any? (sre-sequence (cdr sre))))
             ((seq : $ submatch => submatch-named)
              (and (pair? (cdr sre)) (sre-searcher? (cadr sre))))
             ((or) (every sre-searcher? (cdr sre)))
             (else #f)))))

;; a consumer doesn't need to match more than once
(define (sre-consumer? sre)
  (or (sre-bos? sre)
      (and (pair? sre)
           (case (car sre)
             ((* +) (sre-any? (sre-sequence (cdr sre))))
             ((seq : $ submatch => submatch-named)
              (and (pair? (cdr sre)) (sre-consumer? (last sre))))
             ((or) (every sre-consumer? (cdr sre)))
             (else #f)))))

(define (sre-has-submatches? sre)
  (and (pair? sre)
       (or (memq (car sre) '($ submatch => submatch-named))
           (if (eq? 'posix-string (car sre))
               (sre-has-submatches? (string->sre (cadr sre)))
               (any sre-has-submatches? (cdr sre))))))

(define (sre-count-submatches sre)
  (let count ((sre sre) (sum 0))
    (if (pair? sre)
        (fold count
              (+ sum (case (car sre)
                       (($ submatch => submatch-named) 1)
                       ((dsm) (+ (cadr sre) (caddr sre)))
                       ((posix-string)
                        (sre-count-submatches (string->sre (cadr sre))))
                       (else 0)))
              (cdr sre))
        sum)))

(define (sre-length-ranges sre . o)
  (let ((names (if (pair? o) (car o) (sre-names sre 1 '())))
        (sublens (make-vector (+ 1 (sre-count-submatches sre)) #f)))
    (vector-set!
     sublens
     0
     (let lp ((sre sre) (n 1) (lo 0) (hi 0) (return cons))
       (define (grow i) (return (+ lo i) (and hi (+ hi i))))
       (cond
        ((pair? sre)
         (if (string? (car sre))
             (grow 1)
             (case (car sre)
               ((/ ~ & -)
                (grow 1))
               ((posix-string)
                (lp (string->sre (cadr sre)) n lo hi return))
               ((seq : w/case w/nocase atomic)
                (let lp2 ((ls (cdr sre)) (n n) (lo2 0) (hi2 0))
                  (if (null? ls)
                      (return (+ lo lo2) (and hi hi2 (+ hi hi2)))
                      (lp (car ls) n 0 0
                          (lambda (lo3 hi3)
                            (lp2 (cdr ls)
                                 (+ n (sre-count-submatches (car ls)))
                                 (+ lo2 lo3)
                                 (and hi2 hi3 (+ hi2 hi3))))))))
               ((or)
                (let lp2 ((ls (cdr sre)) (n n) (lo2 #f) (hi2 0))
                  (if (null? ls)
                      (return (+ lo (or lo2 1)) (and hi hi2 (+ hi hi2)))
                      (lp (car ls) n 0 0
                          (lambda (lo3 hi3)
                            (lp2 (cdr ls)
                                 (+ n (sre-count-submatches (car ls)))
                                 (if lo2 (min lo2 lo3) lo3)
                                 (and hi2 hi3 (max hi2 hi3))))))))
               ((if)
                (cond
                 ((or (null? (cdr sre)) (null? (cddr sre)))
                  (return lo hi))
                 (else
                  (let ((n1 (sre-count-submatches (car sre)))
                        (n2 (sre-count-submatches (cadr sre))))
                    (lp (if (or (number? (cadr sre)) (symbol? (cadr sre)))
                            'epsilon
                            (cadr sre))
                        n lo hi
                        (lambda (lo2 hi2)
                          (lp (caddr sre) (+ n n1) 0 0
                              (lambda (lo3 hi3)
                                (lp (if (pair? (cdddr sre))
                                        (cadddr sre)
                                        'epsilon)
                                    (+ n n1 n2) 0 0
                                    (lambda (lo4 hi4)
                                      (return (+ lo2 (min lo3 lo4))
                                              (and hi2 hi3 hi4
                                                   (+ hi2 (max hi3 hi4))
                                                   ))))))))))))
               ((dsm)
                (lp (sre-sequence (cdddr sre)) (+ n (cadr sre)) lo hi return))
               (($ submatch => submatch-named)
                (lp (sre-sequence
                     (if (eq? 'submatch (car sre)) (cdr sre) (cddr sre)))
                    (+ n 1) lo hi
                    (lambda (lo2 hi2)
                      (vector-set! sublens n (cons lo2 hi2))
                      (return lo2 hi2))))
               ((backref backref-ci)
                (let ((n (cond
                          ((number? (cadr sre)) (cadr sre))
                          ((assq (cadr sre) names) => cdr)
                          (else (error "unknown backreference" (cadr sre))))))
                  (cond
                   ((or (not (integer? n))
                        (not (< 0 n (vector-length sublens))))
                    (error "sre-length: invalid backreference" sre))
                   ((not (vector-ref sublens n))
                    (error "sre-length: invalid forward backreference" sre))
                   (else
                    (let ((lo2 (car (vector-ref sublens n)))
                          (hi2 (cdr (vector-ref sublens n))))
                      (return (+ lo lo2) (and hi hi2 (+ hi hi2))))))))
               ((* *?)
                (lp (sre-sequence (cdr sre)) n lo hi (lambda (lo hi) #f))
                (return lo #f))
               ((** **?)
                (cond
                 ((or (and (number? (cadr sre))
                           (number? (caddr sre))
                           (> (cadr sre) (caddr sre)))
                      (and (not (cadr sre)) (caddr sre)))
                  (return lo hi))
                 (else
                  (if (caddr sre)
                      (lp (sre-sequence (cdddr sre)) n 0 0
                          (lambda (lo2 hi2)
                            (return (+ lo (* (cadr sre) lo2))
                                    (and hi hi2 (+ hi (* (caddr sre) hi2))))))
                      (lp (sre-sequence (cdddr sre)) n 0 0
                          (lambda (lo2 hi2)
                            (return (+ lo (* (cadr sre) lo2)) #f)))))))
               ((+)
                (lp (sre-sequence (cdr sre)) n lo hi
                    (lambda (lo2 hi2)
                      (return (+ lo lo2) #f))))
               ((? ??)
                (lp (sre-sequence (cdr sre)) n lo hi
                    (lambda (lo2 hi2)
                      (return lo (and hi hi2 (+ hi hi2))))))
               ((= =? >= >=?)
                (lp `(** ,(cadr sre)
                         ,(if (memq (car sre) '(>= >=?)) #f (cadr sre))
                         ,@(cddr sre))
                    n lo hi return))
               ((look-ahead neg-look-ahead look-behind neg-look-behind)
                (return lo hi))
               (else
                (cond
                 ((assq (car sre) sre-named-definitions)
                  => (lambda (cell)
                       (lp (apply (cdr cell) (cdr sre)) n lo hi return)))
                 (else
                  (error "sre-length-ranges: unknown sre operator" sre)))))))
        ((char? sre)
         (grow 1))
        ((string? sre)
         (grow (string-length sre)))
        ((memq sre '(any nonl))
         (grow 1))
        ((memq sre '(epsilon bos eos bol eol bow eow nwb commit))
         (return lo hi))
        (else
         (let ((cell (assq sre sre-named-definitions)))
           (if cell
               (lp (if (procedure? (cdr cell)) ((cdr cell)) (cdr cell))
                   n lo hi return)
               (error "sre-length-ranges: unknown sre" sre)))))))
    sublens))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; SRE Manipulation

;; build a (seq ls ...) sre from a list
(define (sre-sequence ls)
  (cond
   ((null? ls) 'epsilon)
   ((null? (cdr ls)) (car ls))
   (else (cons 'seq ls))))

;; build a (or ls ...) sre from a list
(define (sre-alternate ls)
  (cond
   ((null? ls) '(or))
   ((null? (cdr ls)) (car ls))
   (else (cons 'or ls))))

;; returns an equivalent SRE without any match information
(define (sre-strip-submatches sre)
  (if (not (pair? sre))
      sre
      (case (car sre)
        (($ submatch) (sre-strip-submatches (sre-sequence (cdr sre))))
        ((=> submatch-named) (sre-strip-submatches (sre-sequence (cddr sre))))
        ((dsm) (sre-strip-submatches (sre-sequence (cdddr sre))))
        (else (map sre-strip-submatches sre)))))

;; given a char-set list of chars and strings, flattens them into
;; chars only
(define (sre-flatten-ranges ls)
  (let lp ((ls ls) (res '()))
    (cond
     ((null? ls)
      (reverse res))
     ((string? (car ls))
      (lp (append (string->list (car ls)) (cdr ls)) res))
     (else
      (lp (cdr ls) (cons (car ls) res))))))

(define (sre-names sre n names)
  (if (not (pair? sre))
      names
      (case (car sre)
        (($ submatch)
         (sre-names (sre-sequence (cdr sre)) (+ n 1) names))
        ((=> submatch-named)
         (sre-names (sre-sequence (cddr sre))
                    (+ n 1)
                    (cons (cons (cadr sre) n) names)))
        ((dsm)
         (sre-names (sre-sequence (cdddr sre)) (+ n (cadr sre)) names))
        ((seq : or * + ? *? ?? w/case w/nocase atomic
          look-ahead look-behind neg-look-ahead neg-look-behind)
         (sre-sequence-names (cdr sre) n names))
        ((= >=)
         (sre-sequence-names (cddr sre) n names))
        ((** **?)
         (sre-sequence-names (cdddr sre) n names))
        (else
         names))))

(define (sre-sequence-names ls n names)
  (if (null? ls)
      names
      (sre-sequence-names (cdr ls)
                          (+ n (sre-count-submatches (car ls)))
                          (sre-names (car ls) n names))))

(define (sre-remove-initial-bos sre)
  (cond
   ((pair? sre)
    (case (car sre)
      ((seq : $ submatch => submatch-named * +)
       (cond
        ((not (pair? (cdr sre)))
         sre)
        ((eq? 'bos (cadr sre))
         (cons (car sre) (cddr sre)))
        (else
         (cons (car sre)
               (cons (sre-remove-initial-bos (cadr sre)) (cddr sre))))))
      ((or)
       (sre-alternate (map sre-remove-initial-bos (cdr sre))))
      (else
       sre)))
   (else
    sre)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Basic Matching

(define irregex-basic-string-chunker
  (make-irregex-chunker (lambda (x) #f)
                        car
                        cadr
                        caddr
                        (lambda (src1 i src2 j)
                          (substring (car src1) i j))))

(define (irregex-search x str . o)
  (if (not (string? str)) (error "irregex-search: not a string" str))
  (let ((start (or (and (pair? o) (car o)) 0))
        (end (or (and (pair? o) (pair? (cdr o)) (cadr o)) (string-length str))))
    (if (not (and (integer? start) (exact? start)))
        (error "irregex-search: not an exact integer" start))
    (if (not (and (integer? end) (exact? end)))
        (error "irregex-search: not an exact integer" end))
    (irregex-search/chunked x
                            irregex-basic-string-chunker
                            (list str start end)
                            start)))

(define (irregex-search/chunked x cnk src . o)
  (let* ((irx (irregex x))
         (matches (irregex-new-matches irx))
         (i (if (pair? o) (car o) ((chunker-get-start cnk) src))))
    (irregex-match-chunker-set! matches cnk)
    (irregex-search/matches irx cnk (cons src i) src i matches)))

;; internal routine, can be used in loops to avoid reallocating the
;; match vector
(define (irregex-search/matches irx cnk init src i matches)
  (cond
   ((irregex-dfa irx)
    (cond
     ((flag-set? (irregex-flags irx) ~searcher?)
      (cond
       ((dfa-match/longest (irregex-dfa irx) cnk src i #f #f matches 0)
        (irregex-match-start-chunk-set! matches 0 src)
        (irregex-match-start-index-set! matches 0 i)
        matches)
       (else
        #f)))
     ((dfa-match/shortest
       (irregex-dfa/search irx) cnk src i matches 0)
      (let ((dfa (irregex-dfa irx))
            (get-start (chunker-get-start cnk))
            (get-end (chunker-get-end cnk))
            (get-next (chunker-get-next cnk)))
        (let lp1 ((src src) (i i))
          (let ((end (get-end src)))
            (let lp2 ((i i))
              (cond
               ((dfa-match/longest dfa cnk src i #f #f matches 0)
                (irregex-match-start-chunk-set! matches 0 src)
                (irregex-match-start-index-set! matches 0 i)
                matches)
               ((>= i end)
                (let ((next (get-next src)))
                  (and next (lp1 next (get-start next)))))
               (else
                (lp2 (+ i 1)))))))))
     (else
      #f)))
   (else
    (let ((res (irregex-search/backtrack irx cnk init src i matches)))
      (if res (%irregex-match-fail-set! res #f))
      res))))

(define (irregex-search/backtrack irx cnk init src i matches)
  (let ((matcher (irregex-nfa irx))
        (str ((chunker-get-str cnk) src))
        (end ((chunker-get-end cnk) src))
        (get-next (chunker-get-next cnk)))
    (if (flag-set? (irregex-flags irx) ~searcher?)
        (matcher cnk init src str i end matches (lambda () #f))
        (let lp ((src2 src)
                 (str str)
                 (i i)
                 (end end))
          (cond
           ((matcher cnk init src2 str i end matches (lambda () #f))
            (irregex-match-start-chunk-set! matches 0 src2)
            (irregex-match-start-index-set! matches 0 i)
            matches)
           ((< i end)
            (lp src2 str (+ i 1) end))
           (else
            (let ((src2 (get-next src2)))
              (if src2
                  (lp src2
                      ((chunker-get-str cnk) src2)
                      ((chunker-get-start cnk) src2)
                      ((chunker-get-end cnk) src2))
                  #f))))))))

(define (irregex-match irx str . o)
  (if (not (string? str)) (error "irregex-match: not a string" str))
  (let ((start (or (and (pair? o) (car o)) 0))
        (end (or (and (pair? o) (pair? (cdr o)) (cadr o)) (string-length str))))
    (if (not (and (integer? start) (exact? start)))
        (error "irregex-match: not an exact integer" start))
    (if (not (and (integer? end) (exact? end)))
        (error "irregex-match: not an exact integer" end))
    (irregex-match/chunked irx
                           irregex-basic-string-chunker
                           (list str start end))))

(define (irregex-match/chunked irx cnk src)
  (let* ((irx (irregex irx))
         (matches (irregex-new-matches irx)))
    (irregex-match-chunker-set! matches cnk)
    (cond
     ((irregex-dfa irx)
      (and
       (dfa-match/longest
        (irregex-dfa irx) cnk src ((chunker-get-start cnk) src) #f #f matches 0)
       (= ((chunker-get-end cnk) (%irregex-match-end-chunk matches 0))
          (%irregex-match-end-index matches 0))
       (begin
         (irregex-match-start-chunk-set! matches 0 src)
         (irregex-match-start-index-set! matches
                                         0
                                         ((chunker-get-start cnk) src))
         matches)))
     (else
      (let* ((matcher (irregex-nfa irx))
             (str ((chunker-get-str cnk) src))
             (i ((chunker-get-start cnk) src))
             (end ((chunker-get-end cnk) src))
             (init (cons src i)))
        (let lp ((m (matcher cnk init src str i end matches (lambda () #f))))
          (and m
               (cond
                ((and (not ((chunker-get-next cnk)
                            (%irregex-match-end-chunk m 0)))
                      (= ((chunker-get-end cnk)
                          (%irregex-match-end-chunk m 0))
                         (%irregex-match-end-index m 0)))
                 (%irregex-match-fail-set! m #f)
                 m)
                ((%irregex-match-fail m)
                 (lp ((%irregex-match-fail m))))
                (else
                 #f)))))))))

(define (irregex-match? . args)
  (and (apply irregex-match args) #t))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; DFA Matching

;; inline these
(define (dfa-init-state dfa)
  (vector-ref dfa 0))
(define (dfa-next-state dfa node)
  (vector-ref dfa (cadr node)))
(define (dfa-cell-commands dfa node)
  (cddr node))
(define (dfa-finalizer dfa state)
  (car state))

;; this searches for the first end index for which a match is possible
(define (dfa-match/shortest dfa cnk src start matches index)
  (let ((get-str (chunker-get-str cnk))
        (get-start (chunker-get-start cnk))
        (get-end (chunker-get-end cnk))
        (get-next (chunker-get-next cnk))
        ;; Skip the "set-up" state, we don't need to set tags.
        (start-state (dfa-next-state dfa (cadr (dfa-init-state dfa)))))
    (let lp1 ((src src) (start start) (state start-state))
      (and
       src
       (let ((str (get-str src))
             (end (get-end src)))
         (let lp2 ((i start) (state state))
           (cond
            ((dfa-finalizer dfa state)
             (cond
              (index
               (irregex-match-end-chunk-set! matches index src)
               (irregex-match-end-index-set! matches index i)))
             #t)
            ((< i end)
             (let* ((ch (string-ref str i))
                    (next (find (lambda (x)
                                  (or (eqv? ch (car x))
                                      (and (not (char? (car x)))
                                           (cset-contains? (car x) ch))))
                                (cdr state))))
               (and next (lp2 (+ i 1) (dfa-next-state dfa next)))))
            (else
             (let ((next (get-next src)))
               (and next (lp1 next (get-start next) state)))))))))))

(define (finalize! finalizer memory matches)
  (for-each
   (lambda (tag&slot)
     (let* ((tag (car tag&slot))
            (slot (vector-ref memory (cdr tag&slot)))
            (chunk&pos (vector-ref slot tag)))
       (irregex-match-chunk&index-from-tag-set!
        matches tag
        (and chunk&pos (car chunk&pos))
        (and chunk&pos (cdr chunk&pos)))))
   finalizer))
(define (make-initial-memory slots matches)
  (let ((size (* (irregex-match-num-submatches matches) 2))
        (memory (make-vector slots)))
    (do ((i 0 (+ i 1)))
        ((= i slots) memory)
      (vector-set! memory i (make-vector size #f)))))

;; this finds the longest match starting at a given index
(define (dfa-match/longest dfa cnk src start end-src end matches index)
  (let* ((get-str (chunker-get-str cnk))
         (get-start (chunker-get-start cnk))
         (get-end (chunker-get-end cnk))
         (get-next (chunker-get-next cnk))
         (initial-state (dfa-init-state dfa))
         (memory-size (car initial-state))
         (submatches? (not (zero? memory-size)))
         ;; A vector of vectors, each of size <number of start/end submatches>
         (memory (make-initial-memory memory-size matches))
         (init-cell (cadr initial-state))
         (start-state (dfa-next-state dfa init-cell))
         (start-finalizer (dfa-finalizer dfa start-state)))
    (cond
     (index
      (irregex-match-end-chunk-set! matches index #f)
      (irregex-match-end-index-set! matches index #f)))
    (cond (submatches?
           (for-each (lambda (s)
                       (let ((slot (vector-ref memory (cdr s))))
                         (vector-set! slot (car s) (cons src start))))
                     (cdr (dfa-cell-commands dfa init-cell)))))
    (let lp1 ((src src)
              (start start)
              (state start-state)
              (res-src (and start-finalizer src))
              (res-index (and start-finalizer start))
              (finalizer start-finalizer))
      (let ((str (get-str src))
            (end (if (eq? src end-src) end (get-end src))))
        (let lp2 ((i start)
                  (state state)
                  (res-src res-src)
                  (res-index res-index)
                  (finalizer finalizer))
          (cond
           ((>= i end)
            (cond
             ((and index res-src)
              (irregex-match-end-chunk-set! matches index res-src)
              (irregex-match-end-index-set! matches index res-index)))
            (let ((next (and (not (eq? src end-src)) (get-next src))))
              (if next
                  (lp1 next (get-start next) state res-src res-index finalizer)
                  (and index
                       (%irregex-match-end-chunk matches index)
                       (or (not finalizer) (finalize! finalizer memory matches))
                       #t))))
           (else
            (let* ((ch (string-ref str i))
                   (cell (find (lambda (x)
                                 (or (eqv? ch (car x))
                                     (and (not (char? (car x)))
                                          (cset-contains? (car x) ch))))
                               (cdr state))))
              (cond
               (cell
                (let* ((next (dfa-next-state dfa cell))
                       (new-finalizer (dfa-finalizer dfa next)))
                  (cond
                   (submatches?
                    (let ((cmds (dfa-cell-commands dfa cell)))
                      ;; Save match when we're moving from accepting state to
                      ;; rejecting state; this could be the last accepting one.
                      (cond ((and finalizer (not new-finalizer))
                             (finalize! finalizer memory matches)))
                      (for-each (lambda (s)
                                  (let ((slot (vector-ref memory (cdr s)))
                                        (chunk&position (cons src (+ i 1))))
                                    (vector-set! slot (car s) chunk&position)))
                                (cdr cmds))
                      ;; Reassigning commands may be in an order which
                      ;; causes memory cells to be clobbered before
                      ;; they're read out.  Make 2 passes to maintain
                      ;; old values by copying them into a closure.
                      (for-each (lambda (execute!) (execute!))
                                (map (lambda (c)
                                       (let* ((tag (vector-ref c 0))
                                              (ss (vector-ref memory (vector-ref c 1)))
                                              (ds (vector-ref memory (vector-ref c 2)))
                                              (value-from (vector-ref ss tag)))
                                         (lambda () (vector-set! ds tag value-from))))
                                     (car cmds))))))
                  (if new-finalizer
                      (lp2 (+ i 1) next src (+ i 1) new-finalizer)
                      (lp2 (+ i 1) next res-src res-index #f))))
               (res-src
                (cond
                 (index
                  (irregex-match-end-chunk-set! matches index res-src)
                  (irregex-match-end-index-set! matches index res-index)))
                (cond (finalizer (finalize! finalizer memory matches)))
                #t)
               ((and index (%irregex-match-end-chunk matches index))
                (cond (finalizer (finalize! finalizer memory matches)))
                #t)
               (else
                #f))))))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Named Definitions

(define sre-named-definitions
  `((any . ,*all-chars*)
    (nonl . (- ,*all-chars* (,(string #\newline))))
    (alphabetic . (/ #\a #\z #\A #\Z))
    (alpha . alphabetic)
    (alphanumeric . (/ #\a #\z #\A #\Z #\0 #\9))
    (alphanum . alphanumeric)
    (alnum . alphanumeric)
    (lower-case . (/ #\a #\z))
    (lower . lower-case)
    (upper-case . (/ #\A #\Z))
    (upper . upper-case)
    (numeric . (/ #\0 #\9))
    (num . numeric)
    (digit . numeric)
    (punctuation . (or #\! #\" #\# #\% #\& #\' #\( #\) #\* #\, #\- #\.
                       #\/ #\: #\; #\? #\@ #\[ #\\ #\] #\_ #\{ #\}))
    (punct . punctuation)
    (graphic
     . (or alphanumeric punctuation #\$ #\+ #\< #\= #\> #\^ #\` #\| #\~))
    (graph . graphic)
    (blank . (or #\space ,(integer->char (- (char->integer #\space) 23))))
    ;; 0B - vertical tab, 0C - form feed
    (whitespace . (or blank #\newline #\x0C #\return #\x0B))
    (space . whitespace)
    (white . whitespace)
    (printing . (or graphic whitespace))
    (print . printing)

    ;; XXXX we assume a (possibly shifted) ASCII-based ordering
    (control . (/ ,(integer->char (- (char->integer #\space) 32))
                  ,(integer->char (- (char->integer #\space) 1))))
    (cntrl . control)
    (hex-digit . (or numeric (/ #\a #\f #\A #\F)))
    (xdigit . hex-digit)
    (ascii . (/ ,(integer->char (- (char->integer #\space) 32))
                ,(integer->char (+ (char->integer #\space) 95))))
    (ascii-nonl . (/ ,(integer->char (- (char->integer #\space) 32))
                     ,(integer->char (- (char->integer #\newline) 1))
                     ,(integer->char (+ (char->integer #\newline) 1))
                     ,(integer->char (+ (char->integer #\space) 95))))
    (newline . (or (seq ,(integer->char (+ (char->integer #\newline) 3))
                        #\newline)
                   (/ #\newline
                      ,(integer->char (+ (char->integer #\newline) 3)))))

    ;; ... it's really annoying to support old Scheme48
    (word . (seq bow (+ (or alphanumeric #\_)) eow))
    (utf8-tail-char . (/ ,(integer->char (+ (char->integer #\space) #x60))
                         ,(integer->char (+ (char->integer #\space) #xA1))))
    (utf8-2-char . (seq (/ ,(integer->char (+ (char->integer #\space) #xA2))
                           ,(integer->char (+ (char->integer #\space) #xBF)))
                        utf8-tail-char))
    (utf8-3-char . (seq (/ ,(integer->char (+ (char->integer #\space) #xC0))
                           ,(integer->char (+ (char->integer #\space) #xCF)))
                        utf8-tail-char
                        utf8-tail-char))
    (utf8-4-char . (seq (/ ,(integer->char (+ (char->integer #\space) #xD0))
                           ,(integer->char (+ (char->integer #\space) #xD7)))
                        utf8-tail-char
                        utf8-tail-char
                        utf8-tail-char))
    (utf8-any . (or ascii utf8-2-char utf8-3-char utf8-4-char))
    (utf8-nonl . (or ascii-nonl utf8-2-char utf8-3-char utf8-4-char))

    ;; extended library patterns
    (integer . (seq (? (or #\+ #\-)) (+ numeric)))
    (real . (seq (? (or #\+ #\-))
                 (+ numeric) (? #\. (+ numeric))
                 (? (or #\e #\E) integer)))
    ;; slightly more lax than R5RS, allow ->foo, etc.
    (symbol-initial . (or alpha ("!$%&*/:<=>?^_~")))
    (symbol-subsequent . (or symbol-initial digit ("+-.@")))
    (symbol . (or (seq symbol-initial (* symbol-subsequent))
                  (seq ("+-") (? symbol-initial (* symbol-subsequent)))
                  (seq ".." (* "."))))
    (sexp-space . (seq (* (* space) ";" (* nonl) newline) (+ space)))
    (string . (seq #\" (escape #\\ #\") #\"))
    (escape . ,(lambda (esc . o) `(* (or (~ ,esc ,@o) (seq ,esc any)))))

    (ipv4-digit . (seq (? (/ "12")) (? numeric) numeric))
    (ipv4-address . (seq ipv4-digit (= 3 #\. ipv4-digit)))
    ;; XXXX lax, allows multiple double-colons or < 8 terms w/o a ::
    (ipv6-address . (seq (** 0 4 hex-digit)
                         (** 1 7 #\: (? #\:) (** 0 4 hex-digit))))
    (ip-address . (or ipv4-address ipv6-address))
    (domain-atom . (+ (or alphanumeric #\_ #\-)))
    (domain . (seq domain-atom (+ #\. domain-atom)))
    ;; XXXX now anything can be a top-level domain, but this is still handy
    (top-level-domain . (w/nocase (or "arpa" "com" "gov" "mil" "net" "org"
                                      "edu" "aero" "biz" "coop" "info"
				      "museum" "name" "pro" (= 2 alpha))))
    (domain/common . (seq (+ domain-atom #\.) top-level-domain))
    ;;(email-local-part . (seq (+ (or (~ #\") string))))
    (email-local-part . (+ (or alphanumeric #\_ #\- #\. #\+)))
    (email . (seq email-local-part #\@ domain))
    (url-char . (or alnum #\_ #\- #\+ #\\ #\= #\~ #\. #\, #\& #\;
                    (seq "%" hex-digit hex-digit)))
    (url-final-char . (or alnum #\_ #\- #\+ #\\ #\= #\~ #\&
                          (seq "%" hex-digit hex-digit)))
    (http-url . (w/nocase
                 "http" (? "s") "://"
                 (or domain ipv4-address) ;; (seq "[" ipv6-address "]")
                 (? ":" (+ numeric)) ;; port
                 ;; path
                 (? "/" (* (or url-char "/"))
                    (? "?" (* url-char))                      ;; query
                    (? "#" (? (* url-char) url-final-char)) ;; fragment
                    )))

    ))


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; SRE->tNFA compilation
;;
;; A tagged NFA (tNFA) state is a numbered node with a list of
;; pattern->number transitions, where pattern is character set range,
;; or epsilon (indicating an empty transition).
;;
;; (Only) epsilon transitions may be *tagged*.  Each tag represents
;; either the start or the end of a submatch.
;;
;; There may be overlapping ranges - since it's an NFA we process it
;; by considering all possible transitions.

(define *nfa-presize* 128)  ;; constant
(define *nfa-num-fields* 4) ;; constant

(define (nfa-num-states nfa) (quotient (vector-length nfa) *nfa-num-fields*))
(define (nfa-start-state nfa) (- (nfa-num-states nfa) 1))

(define (nfa-num-tags nfa)
  (vector-ref nfa 0))
(define (nfa-highest-map-index nfa)
  (vector-ref nfa 1))
(define (nfa-set-highest-map-index! nfa idx)
  (vector-set! nfa 1 idx))

(define (nfa-get-state-trans nfa i)
  (if (= i 0) '() (vector-ref nfa (* i *nfa-num-fields*))))
(define (nfa-set-state-trans! nfa i x)
  (vector-set! nfa (* i *nfa-num-fields*) x))

(define (nfa-get-epsilons nfa i)
  (if (= i 0) '() (vector-ref nfa (+ (* i *nfa-num-fields*) 1))))
(define (nfa-set-epsilons! nfa i x)
  (vector-set! nfa (+ (* i *nfa-num-fields*) 1) x))
(define (nfa-add-epsilon! nfa i x t)
  (let ((eps (nfa-get-epsilons nfa i)))
    (if (not (assv x eps))
        (nfa-set-epsilons! nfa i (cons (cons x t) eps)))))

(define (nfa-get-reorder-commands nfa mst)
  (cond ((assoc mst (vector-ref nfa (+ (* (mst-hash mst) *nfa-num-fields*) 2)))
         => cdr)
        (else #f)))
(define (nfa-set-reorder-commands! nfa mst x)
  (let ((i (+ (* (mst-hash mst) *nfa-num-fields*) 2)))
    (vector-set! nfa i (cons (cons mst x) (vector-ref nfa i)))))

(define (nfa-get-closure nfa mst)
  (cond ((assoc mst (vector-ref nfa (+ (* (mst-hash mst) *nfa-num-fields*) 3)))
         => cdr)
        (else #f)))
(define (nfa-add-closure! nfa mst x)
  (let ((i (+ (* (mst-hash mst) *nfa-num-fields*) 3)))
    (vector-set! nfa i (cons (cons mst x) (vector-ref nfa i)))))

;; Compile and return the vector of NFA states (in groups of
;; *nfa-num-fields* packed elements).  The start state will be the
;; last element(s) of the vector, and all remaining states will be in
;; descending numeric order, with state 0 being the unique accepting
;; state.
(define (sre->nfa sre init-flags)
  (let* ((buf (make-vector (* *nfa-presize* *nfa-num-fields*) '()))
         ;; Get cons cells and map them to numeric submatch indexes.
         ;; Doing it here is slightly easier than integrating into the loop below
         (match-index
          (let lp ((sre (list sre)) (max 0) (res '()))
            (cond
             ((not (pair? sre))
              ;; We abuse the transitions slot for state 0 (the final state,
              ;; which can have no transitions) to store the number of tags.
              (vector-set! buf 0 (* max 2))
              ;; We abuse the epsilons slot for state 0 to store the highest
              ;; encountered memory slot mapping index.  Initialize to -1.
              (vector-set! buf 1 -1)
              res)
             ((pair? (car sre))
              ;; The appends here should be safe (are they?)
              (case (caar sre)
                (($ submatch => submatch-named)
                 (lp (append (cdar sre) (cdr sre)) (+ max 1)
                     (cons (cons (car sre) max) res)))
                (else (lp (append (car sre) (cdr sre)) max res))))
             (else (lp (cdr sre) max res))))))
    ;; we loop over an implicit sequence list
    (define (lp ls n flags next)
      (define (new-state-number state)
        (max n (+ 1 state)))
      (define (add-state! n2 trans-ls)
        (if (>= (* n2 *nfa-num-fields*) (vector-length buf))
            (let ((tmp (make-vector (* 2 (vector-length buf)) '())))
              (do ((i (- (vector-length buf) 1) (- i 1)))
                  ((< i 0))
                (vector-set! tmp i (vector-ref buf i)))
              (set! buf tmp)))
        (nfa-set-state-trans! buf n2 trans-ls)
        n2)
      (define (extend-state! next trans-cs)
        (and next
             (add-state! (new-state-number next) (cons trans-cs next))))
      (define (add-char-state! next ch)
        (let ((alt (char-altcase ch)))
          (if (flag-set? flags ~case-insensitive?)
              (extend-state! next (cset-union (char->cset ch) (char->cset alt)))
              (extend-state! next (char->cset ch)))))
      (if (null? ls)
          next
          (cond
           ((or (eq? 'epsilon (car ls)) (equal? "" (car ls)))
            ;; chars and epsilons go directly into the transition table
            (let ((next (lp (cdr ls) n flags next)))
              (and next
                   (let ((new (add-state! (new-state-number next) '())))
                     (nfa-add-epsilon! buf new next #f)
                     new))))
           ((string? (car ls))
            ;; process literal strings a char at a time
            (let ((next (lp (cdr ls) n flags next)))
              (and next
                   (let lp2 ((i (- (string-length (car ls)) 1))
                             (next next))
                     (if (< i 0)
                         next
                         (lp2 (- i 1)
                              (add-char-state! next (string-ref (car ls) i))))
                     ))))
           ((char? (car ls))
            (add-char-state! (lp (cdr ls) n flags next) (car ls)))
           ((symbol? (car ls))
            (let ((cell (assq (car ls) sre-named-definitions)))
              (and cell
                   (lp (cons (if (procedure? (cdr cell))
                                 ((cdr cell))
                                 (cdr cell))
                             (cdr ls))
                       n
                       flags
                       next))))
           ((pair? (car ls))
            (cond
             ((string? (caar ls))       ; Enumerated character set
              (let ((set (if (flag-set? flags ~case-insensitive?)
                             (cset-case-insensitive (string->cset (caar ls)))
                             (string->cset (caar ls)))))
               (extend-state! (lp (cdr ls) n flags next) set)))
             (else
              (case (caar ls)
                ((seq :)
                 ;; for an explicit sequence, just append to the list
                 (lp (append (cdar ls) (cdr ls)) n flags next))
                ((w/case w/nocase w/utf8 w/noutf8)
                 (let* ((next (lp (cdr ls) n flags next))
                        (flags ((if (memq (caar ls) '(w/case w/utf8))
                                    flag-clear
                                    flag-join)
                                flags
                                (if (memq (caar ls) '(w/case w/nocase))
                                    ~case-insensitive?
                                    ~utf8?))))
                   (and next
                        (lp (cdar ls) (new-state-number next) flags next))))
                ((/ - & ~)
                 (let ((range (sre->cset (car ls)
                                         (flag-set? flags ~case-insensitive?))))
                   (extend-state! (lp (cdr ls) n flags next)
                                  range)))
                ((or)
                 (let ((next (lp (cdr ls) n flags next)))
                   (and
                    next
                    (if (null? (cdar ls))
                        ;; empty (or) always fails
                        (add-state! (new-state-number next) '())
                        ;; compile both branches and insert epsilon
                        ;; transitions to either
                        (let* ((b (lp (list (sre-alternate (cddar ls)))
                                      (new-state-number next)
                                      flags
                                      next))
                               (a (and b
                                       (lp (list (cadar ls))
                                           (new-state-number (max b next))
                                           flags
                                           next))))
                          (and a
                               (let ((c (add-state! (new-state-number (max a b))
                                                    '())))
                                 (nfa-add-epsilon! buf c a #f)
                                 (nfa-add-epsilon! buf c b #f)
                                 c)))))))
                ((?)
                 (let ((next (lp (cdr ls) n flags next)))
                   ;; insert an epsilon transition directly to next
                   (and
                    next
                    (let ((a (lp (cdar ls) (new-state-number next) flags next)))
                      (if a
                          (nfa-add-epsilon! buf a next #f))
                      a))))
                ((+ *)
                 (let ((next (lp (cdr ls) n flags next)))
                   (and
                    next
                    (let* ((new (lp '(epsilon)
                                    (new-state-number next)
                                    flags
                                    next))
                           (a (lp (cdar ls) (new-state-number new) flags new)))
                      (cond
                       (a
                        ;; for *, insert an epsilon transition as in ? above
                        (if (eq? '* (caar ls))
                            (nfa-add-epsilon! buf a new #f))
                        ;; for both, insert a loop back to self
                        (nfa-add-epsilon! buf new a #f)))
                      a))))
                ;; need to add these to the match extractor first,
                ;; but they tend to generate large DFAs
                ;;((=)
                ;; (lp (append (vector->list
                ;;              (make-vector (cadar ls)
                ;;                           (sre-sequence (cddar ls))))
                ;;             (cdr ls))
                ;;     n flags next))
                ;;((>=)
                ;; (lp (append (vector->list
                ;;              (make-vector (- (cadar ls) 1)
                ;;                           (sre-sequence (cddar ls))))
                ;;             (cons `(+ ,@(cddar ls)) (cdr ls)))
                ;;     n flags next))
                ;;((**)
                ;; (lp (append (vector->list
                ;;              (make-vector (cadar ls)
                ;;                           (sre-sequence (cdddar ls))))
                ;;             (map
                ;;              (lambda (x) `(? ,x))
                ;;              (vector->list
                ;;               (make-vector (- (caddar ls) (cadar ls))
                ;;                            (sre-sequence (cdddar ls)))))
                ;;             (cdr ls))
                ;;     n flags next))
                ;; ignore submatches altogether
                (($ submatch)
                 (let* ((pre-tag (* (cdr (assq (car ls) match-index)) 2))
                        (post-tag (+ pre-tag 1))
                        (next (lp (cdr ls) n flags next)))
                   (and next
                        (let* ((after (add-state! (new-state-number next) '()))
                               (sub (lp (list (sre-sequence (cdar ls)))
                                        (new-state-number after) flags after))
                               (before (and sub (add-state! (new-state-number sub) '()))))
                          (cond (before
                                 (nfa-add-epsilon! buf before sub pre-tag)
                                 (nfa-add-epsilon! buf after next post-tag)))
                          before))))
                ((=> submatch-named)
                 (let* ((pre-tag (* (cdr (assq (car ls) match-index)) 2))
                        (post-tag (+ pre-tag 1))
                        (next (lp (cdr ls) n flags next)))
                   (and next
                        (let* ((after (add-state! (new-state-number next) '()))
                               (sub (lp (list (sre-sequence (cddar ls)))
                                        (new-state-number after) flags after))
                               (before (and sub (add-state! (new-state-number sub) '()))))
                          (cond (before
                                 (nfa-add-epsilon! buf before sub pre-tag)
                                 (nfa-add-epsilon! buf after next post-tag)))
                          before))))
                (else
                 (cond
                  ((assq (caar ls) sre-named-definitions)
                   => (lambda (cell)
                        (if (procedure? (cdr cell))
                            (lp (cons (apply (cdr cell) (cdar ls)) (cdr ls))
                                n flags next)
                            (error "non-procedure in op position" (caar ls)))))
                  (else #f)))))))
           (else
            #f))))
    (let ((len (lp (list sre) 1 init-flags 0)))
      (and len
           (let ((nfa (make-vector (* *nfa-num-fields* (+ len 1)))))
             (do ((i (- (vector-length nfa) 1) (- i 1)))
                 ((< i 0))
               (vector-set! nfa i (vector-ref buf i)))
             nfa)))))

;; We don't really want to use this, we use the closure compilation
;; below instead, but this is included for reference and testing the
;; sre->nfa conversion.

;; (define (nfa-match nfa str)
;;   (let ((matches (make-vector (nfa-num-tags nfa) #f)))
;;     (let lp ((pos 0) (ls (string->list str)) (state (nfa-start-state nfa)) (epsilons '()))
;;       (and (or (and (null? ls) (zero? state))
;;                (let ((t (nfa-get-state-trans nfa state)))
;;                  (and (not (null? t)) (not (null? ls))
;;                       (cset-contains? (car t) (car ls))
;;                       (lp (+ pos 1) (cdr ls) (cdr t) '())))
;;                (any (lambda (e)
;;                       (let ((old-matches (vector-copy matches)))
;;                         (cond ((cdr e)
;;                                (vector-set! matches (cdr e) pos)))
;;                         (or (and (not (memv (car e) epsilons))
;;                                  (lp pos ls (car e) (cons (car e) epsilons)))
;;                             ;; reset match, apparently this branch failed
;;                             (begin (set! matches old-matches) #f))))
;;                     (nfa-get-epsilons nfa state)))
;;            matches))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; NFA multi-state representation

(define *mst-first-state-index* 3)

(define (mst-mappings-summary mst)
  (vector-ref mst 0))

(define (mst-num-states mst)
  (vector-ref mst 1))

(define (mst-num-states-set! mst num)
  (vector-set! mst 1 num))

(define (mst-hash mst)
  ;; We could do (modulo X (nfa-num-states nfa)) here which would be faster,
  ;; but we can't assume a full numerical tower (and updating *could*
  ;; produce a bignum), so we do it each time when updating the hash.
  (vector-ref mst 2))

(define (mst-hash-set! mst hash)
  (vector-set! mst 2 hash))

;; Returns #f if NFA state does not occur in multi-state
(define (mst-state-mappings mst state)
  (vector-ref mst (+ state *mst-first-state-index*)))

(define (mst-state-mappings-set! mst state mappings)
  (vector-set! mst (+ state *mst-first-state-index*) mappings))

;; A multi-state holds a set of states with their tag-to-slot mappings.
;; Slot 0 contains a summary of all mappings for all states in the multi-state.
;; Slot 1 contains the total number of states in the multi-state.
;; Slot 2 contains a hash value, which is used for quick lookup of cached
;; reorder-commands or epsilon-closure in the NFA.  This is the sum of all
;; state numbers plus each tag value (once per occurrence).  This is a silly
;; hashing calculation, but it seems to produce a well-spread out hash table and
;; it has the added advantage that we can use the value as a quick check if the
;; state is definitely NOT equivalent to another in mst-same-states?
;; The other slots contain mappings for each corresponding state.

(define (make-mst nfa)
  (let ((mst (make-vector (+ (nfa-num-states nfa) *mst-first-state-index*) #f)))
    (vector-set! mst 0 (make-vector (nfa-num-tags nfa) '())) ; tag summary
    (vector-set! mst 1 0)               ; total number of states
    (vector-set! mst 2 0)               ; states and tags hash
    mst))

;; NOTE: This doesn't do a deep copy of the mappings.  Don't mutate them!
(define (mst-copy mst)
  (let ((v (vector-copy mst)))
    (vector-set! v 0 (vector-copy (vector-ref mst 0)))
    v))

(define (nfa-state->mst nfa state mappings)
  (let ((mst (make-mst nfa)))
    (mst-add! nfa mst state mappings)
    mst))

;; Extend multi-state with a state and add its tag->slot mappings.
(define (mst-add! nfa mst state mappings)
  (let ((hash-value (mst-hash mst)))
    (cond ((not (mst-state-mappings mst state)) ;  Update state hash & count?
           (set! hash-value (+ hash-value state))
           (mst-num-states-set! mst (+ (mst-num-states mst) 1))))
    (mst-state-mappings-set! mst state mappings)
    (let ((all-mappings (mst-mappings-summary mst)))
      (for-each
       (lambda (tag&slot)
         (let* ((t (car tag&slot))
                (s (cdr tag&slot))
                (m (vector-ref all-mappings t)))
           (cond ((not (memv s m))
                  (set! hash-value (+ hash-value t))
                  (vector-set! all-mappings t (cons s m))))))
       mappings))
    (mst-hash-set! mst (modulo hash-value (nfa-num-states nfa)))))

;; Same as above, but skip updating mappings summary.
;; Called when we know all the tag->slot mappings are already in the summary.
(define (mst-add/fast! nfa mst state mappings)
  (cond ((not (mst-state-mappings mst state)) ;  Update state hash & count?
         (mst-hash-set!
          mst (modulo (+ (mst-hash mst) state)
                      (nfa-num-states nfa)))
         (mst-num-states-set! mst (+ (mst-num-states mst) 1))))
  (mst-state-mappings-set! mst state mappings))

;; Same as above, assigning a new slot for a tag.  This slot is then
;; added to the summary, if it isn't in there yet.  This is more efficient
;; than looping through all the mappings.
(define (mst-add-tagged! nfa mst state mappings tag slot)
  (let* ((mappings-summary (mst-mappings-summary mst))
         (summary-tag-slots (vector-ref mappings-summary tag))
         (new-mappings (let lp ((m mappings)
                                (res '()))
                         (cond ((null? m) (cons (cons tag slot) res))
                               ((= (caar m) tag)
                                (append res (cons (cons tag slot) (cdr m))))
                               (else (lp (cdr m) (cons (car m) res))))))
         (hash-value (mst-hash mst)))
    (cond ((not (mst-state-mappings mst state)) ;  Update state hash & count?
           (set! hash-value (+ hash-value state))
           (mst-num-states-set! mst (+ (mst-num-states mst) 1))))
    (mst-state-mappings-set! mst state new-mappings)
    (cond ((not (memv slot summary-tag-slots)) ; Update tag/slot summary
           (set! hash-value (+ hash-value tag))
           (vector-set! mappings-summary tag (cons slot summary-tag-slots))))
    (mst-hash-set! mst (modulo hash-value (nfa-num-states nfa)))
    new-mappings))

(define (mst-same-states? a b)
  ;; First check if hash and state counts match, then check each state
  (and (= (mst-hash a) (mst-hash b))
       (= (mst-num-states a) (mst-num-states b))
       (let ((len (vector-length a)))
         (let lp ((i *mst-first-state-index*))
           (or (= i len)
               (and (equal? (not (vector-ref a i))
                            (not (vector-ref b i)))
                    (lp (+ i 1))))))))

(define (mst-fold mst kons knil)
  (let ((limit (vector-length mst)))
    (let lp ((i *mst-first-state-index*)
             (acc knil))
      (if (= i limit)
          acc
          (let ((m (vector-ref mst i)))
            (lp (+ i 1) (if m (kons (- i *mst-first-state-index*) m acc) acc)))))))

;; Find the lowest fresh index for this tag that's unused
;; in the multi-state.  This also updates the nfa's highest
;; tag counter if a completely new slot number was assigned.
(define (next-index-for-tag! nfa tag mst)
  (let* ((highest (nfa-highest-map-index nfa))
         (tag-slots (vector-ref (mst-mappings-summary mst) tag))
         (new-index (do ((slot 0 (+ slot 1)))
                        ((not (memv slot tag-slots)) slot))))
    (cond ((> new-index highest)
           (nfa-set-highest-map-index! nfa new-index)))
    new-index))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; tNFA->DFA compilation
;; During processing, the DFA is a list of the form:
;;
;;   ((annotated-tNFA-states ...) finalizer transitions ...)
;;
;; where the transitions are as in the NFA, except there are no
;; epsilons, duplicate characters or overlapping char-set ranges, and
;; the states moved to are closures (sets of NFA states).  Multiple
;; DFA states may be accepting states.  If the state is an accepting state,
;; the finalizer is a list of (tag . memory-slot) retrieval commands.
;; tNFA-states are annotated with mappings which store the tag values of
;; memory slots, if any.  There is always at most one slot for a tag.
;;
;; The DFA itself simulates a NFA by representing all the simultaneous
;; states the NFA can be in at any given point in time as one DFA state.
;; The tag values are ambiguous since each NFA transition can set a tag.
;; To solve this we keep a bank of memory slots around which tracks tag
;; values for each distinct path through the NFA.
;;
;; Once we get to a final state we can pluck the tag values from the
;; memory slots corresponding to the path through which the NFA could have
;; reached the final state.  To resolve ambiguities, states are assigned
;; priorities, and the path to the final state is chosen correspondingly.
;;
;; For a more detailed explanation about this process, see
;; Ville Laurikari; ``NFAs with Tagged Transitions, their Conversion to
;; Deterministic Automata and Application to Regular Expressions'' (2000).
;; Laurikari also wrote a master's thesis about this approach which is
;; less terse but the algorithms are not exactly the same.
;; ``Efficient submatch addressing for regular expressions'' (2001).
;; This implementation follows the 2000 paper where they differ.

(define (nfa->dfa nfa . o)
  (let* ((max-states (and (pair? o) (car o)))
         (start (nfa-state->mst nfa (nfa-start-state nfa) '()))
         (start-closure (nfa-epsilon-closure nfa start))
         ;; Set up a special "initializer" state from which we reach the
         ;; start-closure to ensure that leading tags are set properly.
         (init-set (tag-set-commands-for-closure nfa start start-closure '()))
         (dummy (make-mst nfa))
         (init-state (list dummy #f `((,start-closure #f () . ,init-set)))))
    ;; Unmarked states are just sets of NFA states with tag-maps, marked states
    ;; are sets of NFA states with transitions to sets of NFA states
    (let lp ((unmarked-states (list start-closure))
             (marked-states (list init-state))
             (dfa-size 0))
      (cond
       ((null? unmarked-states)
        ;; Abuse finalizer slot for storing the number of memory slots we need
        (set-car! (cdr init-state) (+ (nfa-highest-map-index nfa) 1))
        (dfa-renumber (reverse marked-states)))
       ((and max-states (> dfa-size max-states)) ; Too many DFA states
        #f)
       ((assoc (car unmarked-states) marked-states) ; Seen set of NFA-states?
        (lp (cdr unmarked-states) marked-states dfa-size))
       (else
        (let ((dfa-state (car unmarked-states)))
          (let lp2 ((trans (get-distinct-transitions nfa dfa-state))
                    (unmarked-states (cdr unmarked-states))
                    (dfa-trans '()))
            (if (null? trans)
                (let ((finalizer (mst-state-mappings dfa-state 0)))
                  (lp unmarked-states
                      (cons (list dfa-state finalizer dfa-trans) marked-states)
                      (+ dfa-size 1)))
                (let* ((closure (nfa-epsilon-closure nfa (cdar trans)))
                       (reordered
                        (find-reorder-commands nfa closure marked-states))
                       (copy-cmds (if reordered (cdr reordered) '()))
                       ;; Laurikari doesn't mention what "k" is, but it seems it
                       ;; must be the mappings of the state's reach
                       (set-cmds (tag-set-commands-for-closure
                                  nfa (cdar trans) closure copy-cmds))
                       (trans-closure (if reordered (car reordered) closure)))
                  (lp2 (cdr trans)
                       (if reordered
                           unmarked-states
                           (cons trans-closure unmarked-states))
                       (cons `(,trans-closure
                               ,(caar trans) ,copy-cmds . ,set-cmds)
                             dfa-trans)))))))))))

;; When the conversion is complete we renumber the DFA sets-of-states
;; in order and convert the result to a vector for fast lookup.
;; Charsets containing single characters are converted to those characters
;; for quick matching of the literal parts in a regex.
(define (dfa-renumber states)
  (let ((indexes (let lp ((i 0) (states states) (indexes '()))
                   (if (null? states)
                       indexes
                       (lp (+ i 1) (cdr states)
                           (cons (cons (caar states) i) indexes)))))
        (dfa (make-vector (length states))))
    (do ((i 0 (+ i 1))
         (states states (cdr states)))
        ((null? states) dfa)
      (let ((maybe-finalizer (cadar states))
            (transitions (caddar states)))
       (vector-set!
        dfa i
        (cons maybe-finalizer
              (map (lambda (tr)
                     `(,(and (cadr tr) (maybe-cset->char (cadr tr)))
                       ,(cdr (assoc (car tr) indexes)) . ,(cddr tr)))
                   transitions)))))))

;; Extract all distinct ranges and the potential states they can transition
;; to from a given set of states.  Any ranges that would overlap with
;; distinct characters are split accordingly.
;; This function is like "reach" in Laurikari's papers, but for each
;; possible distinct range of characters rather than per character.
(define (get-distinct-transitions nfa annotated-states)
  (define (csets-intersect? a b)
    (let ((i (cset-intersection a b)))
      (and (not (cset-empty? i)) i)))
  (mst-fold
   annotated-states
   (lambda (st mappings res)
     (let ((trans (nfa-get-state-trans nfa st))) ; Always one state per trans
       (if (null? trans)
           res
           (let lp ((ls res) (cs (car trans)) (state (cdr trans)) (res '()))
             (cond
              ;; State not seen yet?  Add a new state transition
              ((null? ls)
               ;; TODO: We should try to find an existing DFA state
               ;; with only this NFA state in it, and extend the cset
               ;; with the current one.  This produces smaller DFAs,
               ;; but takes longer to compile.
               (cons (cons cs (nfa-state->mst nfa state mappings))
                     res))
              ((cset=? cs (caar ls))
               ;; Add state to existing set for this charset
               (mst-add! nfa (cdar ls) state mappings)
               (append ls res))
              ((csets-intersect? cs (caar ls)) =>
               (lambda (intersection)
                 (let* ((only-in-new (cset-difference cs (caar ls)))
                        (only-in-old (cset-difference (caar ls) cs))
                        (states-in-both (cdar ls))
                        (states-for-old
                         (and (not (cset-empty? only-in-old))
                              (mst-copy states-in-both)))
                        (res (if states-for-old
                                 (cons (cons only-in-old states-for-old) res)
                                 res)))
                   (mst-add! nfa states-in-both state mappings)
                   ;; Add this state to the states already here and
                   ;; restrict to the overlapping charset and continue
                   ;; with the remaining subset of the new cset (if
                   ;; nonempty)
                   (if (cset-empty? only-in-new)
                       (cons (cons intersection states-in-both)
                             (append (cdr ls) res))
                       (lp (cdr ls) only-in-new state
                           (cons (cons intersection states-in-both) res))))))
              (else
               (lp (cdr ls) cs state (cons (car ls) res))))))))
   '()))

;; The epsilon-closure of a set of states is all the states reachable
;; through epsilon transitions, with the tags encountered on the way.
(define (nfa-epsilon-closure-internal nfa annotated-states)
  ;; The stack _MUST_ be in this order for some reason I don't fully understand
  (let lp ((stack (mst-fold annotated-states
                                        (lambda (st m res)
                                          (cons (cons st m) res))
                                        '()))
           (priorities (make-vector (nfa-num-states nfa) 0))
           (closure (mst-copy annotated-states)))
    (if (null? stack)
        closure
        (let ((prio/orig-state (caar stack)) ; priority is just the state nr.
              (mappings (cdar stack)))
          (let lp2 ((trans (nfa-get-epsilons nfa prio/orig-state))
                    (stack (cdr stack)))
            (if (null? trans)
                (lp stack priorities closure)
                (let ((state (caar trans)))
                  (cond
                   ;; Our priorities are inverted because we start at
                   ;; the highest state number and go downwards to 0.
                   ((> prio/orig-state (vector-ref priorities state))
                    (vector-set! priorities state prio/orig-state)
                    (cond
                     ((cdar trans) =>   ; tagged transition?
                      (lambda (tag)
                       (let* ((index (next-index-for-tag! nfa tag closure))
                              (new-mappings
                               (mst-add-tagged!
                                nfa closure state mappings tag index)))
                         (lp2 (cdr trans)
                              (cons (cons state new-mappings) stack)))))
                     (else
                      (mst-add/fast! nfa closure state mappings)
                      (lp2 (cdr trans) (cons (cons state mappings) stack)))))
                   (else (lp2 (cdr trans) stack))))))))))

(define (nfa-epsilon-closure nfa states)
  (or (nfa-get-closure nfa states)
      (let ((res (nfa-epsilon-closure-internal nfa states)))
        (nfa-add-closure! nfa states res)
        res)))

;; Generate "set" commands for all tags in the closure that are
;; not present in the original state.
(define (tag-set-commands-for-closure nfa orig-state closure copy-cmds)
  (let ((num-tags (nfa-num-tags nfa))
        (closure-summary (mst-mappings-summary closure))
        (state-summary (mst-mappings-summary orig-state)))
    (let lp ((t 0) (cmds '()))
      (if (= t num-tags)
          cmds
          (let lp2 ((s1 (vector-ref closure-summary t))
                    (s2 (vector-ref state-summary t))
                    (cmds cmds))
            (cond ((null? s1) (lp (+ t 1) cmds))
                  ((or (memv (car s1) s2) ; Tag in original state?
                       ;; Try to avoid generating set-commands for any slots
                       ;; that will be overwritten by copy commands, but only
                       ;; if that slot isn't copied to another slot.
                       (and (not (null? copy-cmds)) ; null check for performance
                            ;; Look for copy command overwriting this tag-slot
                            (any (lambda (c)
                                   (and (= (vector-ref c 0) t)
                                        (= (vector-ref c 2) (car s1))))
                                 copy-cmds)
                            ;; Ensure it's not copied to another slot before
                            ;; discarding the set-command.
                            (not (any (lambda (c)
                                        (and (= (vector-ref c 0) t)
                                             (= (vector-ref c 1) (car s1))))
                                      copy-cmds))))
                   (lp2 (cdr s1) s2 cmds))
                  (else (lp2 (cdr s1) s2
                             (cons (cons t (car s1)) cmds)))))))))

;; Look in dfa-states for an already existing state which matches
;; closure, but has different tag value mappings.
;; If found, calculate reordering commands so we can map the closure
;; to that state instead of adding a new DFA state.
;; This is completely handwaved away in Laurikari's paper (it basically
;; says "insert reordering algorithm here"), so this code was constructed
;; after some experimentation.  In other words, bugs be here.
(define (find-reorder-commands-internal nfa closure dfa-states)
  (let ((num-tags (nfa-num-tags nfa))
        (closure-summary (mst-mappings-summary closure)))
    (let lp ((dfa-states dfa-states))
      (if (null? dfa-states)
          #f
          (if (not (mst-same-states? (caar dfa-states) closure))
              (lp (cdr dfa-states))
              (let lp2 ((state-summary (mst-mappings-summary (caar dfa-states)))
                        (t 0) (cmds '()))
                (if (= t num-tags)
                    (cons (caar dfa-states) cmds)
                    (let lp3 ((closure-slots (vector-ref closure-summary t))
                              (state-slots (vector-ref state-summary t))
                              (cmds cmds))
                      (cond ((null? closure-slots)
                             (if (null? state-slots)
                                 (lp2 state-summary (+ t 1) cmds)
                                 (lp (cdr dfa-states))))
                            ((null? state-slots) (lp (cdr dfa-states)))
                            (else (lp3 (cdr closure-slots)
                                       (cdr state-slots)
                                       (if (= (car closure-slots) (car state-slots))
                                           cmds
                                           (cons (vector t (car closure-slots) (car state-slots))
                                                 cmds)))))))))))))

(define (find-reorder-commands nfa closure dfa-states)
  (or (nfa-get-reorder-commands nfa closure)
      (let ((res (find-reorder-commands-internal nfa closure dfa-states)))
        (nfa-set-reorder-commands! nfa closure res)
        res)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Closure Compilation
;;
;; We use this for non-regular expressions instead of an interpreted
;; NFA matcher.  We use backtracking anyway, but this gives us more
;; freedom of implementation, allowing us to support patterns that
;; can't be represented in the above NFA representation.

(define (sre->procedure sre . o)
  (define names
    (if (and (pair? o) (pair? (cdr o))) (cadr o) (sre-names sre 1 '())))
  (let lp ((sre sre)
           (n 1)
           (flags (if (pair? o) (car o) ~none))
           (next (lambda (cnk init src str i end matches fail)
                   (irregex-match-start-chunk-set! matches 0 (car init))
                   (irregex-match-start-index-set! matches 0 (cdr init))
                   (irregex-match-end-chunk-set! matches 0 src)
                   (irregex-match-end-index-set! matches 0 i)
                   (%irregex-match-fail-set! matches fail)
                   matches)))
    ;; XXXX this should be inlined
    (define (rec sre) (lp sre n flags next))
    (cond
     ((pair? sre)
      (if (string? (car sre))
          (sre-cset->procedure
           (sre->cset (car sre) (flag-set? flags ~case-insensitive?))
           next)
          (case (car sre)
            ((~ - & /)
             (sre-cset->procedure
              (sre->cset sre (flag-set? flags ~case-insensitive?))
              next))
            ((or)
             (case (length (cdr sre))
               ((0) (lambda (cnk init src str i end matches fail) (fail)))
               ((1) (rec (cadr sre)))
               (else
                (let* ((first (rec (cadr sre)))
                       (rest (lp (sre-alternate (cddr sre))
                                 (+ n (sre-count-submatches (cadr sre)))
                                 flags
                                 next)))
                  (lambda (cnk init src str i end matches fail)
                    (first cnk init src str i end matches
                           (lambda ()
                             (rest cnk init src str i end matches fail))))))))
            ((w/case)
             (lp (sre-sequence (cdr sre))
                 n
                 (flag-clear flags ~case-insensitive?)
                 next))
            ((w/nocase)
             (lp (sre-sequence (cdr sre))
                 n
                 (flag-join flags ~case-insensitive?)
                 next))
            ((w/utf8)
             (lp (sre-sequence (cdr sre)) n (flag-join flags ~utf8?) next))
            ((w/noutf8)
             (lp (sre-sequence (cdr sre)) n (flag-clear flags ~utf8?) next))
            ((seq :)
             (case (length (cdr sre))
               ((0) next)
               ((1) (rec (cadr sre)))
               (else
                (let ((rest (lp (sre-sequence (cddr sre))
                                (+ n (sre-count-submatches (cadr sre)))
                                flags
                                next)))
                  (lp (cadr sre) n flags rest)))))
            ((?)
             (let ((body (rec (sre-sequence (cdr sre)))))
               (lambda (cnk init src str i end matches fail)
                 (body cnk init src str i end matches
                       (lambda () (next cnk init src str i end matches fail))))))
            ((??)
             (let ((body (rec (sre-sequence (cdr sre)))))
               (lambda (cnk init src str i end matches fail)
                 (next cnk init src str i end matches
                       (lambda () (body cnk init src str i end matches fail))))))
            ((*)
             (cond
              ((sre-empty? (sre-sequence (cdr sre)))
               (error "invalid sre: empty *" sre))
              (else
               (let ((body (rec (list '+ (sre-sequence (cdr sre))))))
                 (lambda (cnk init src str i end matches fail)
                   (body cnk init src str i end matches
                         (lambda ()
                           (next cnk init src str i end matches fail))))))))
            ((*?)
             (cond
              ((sre-empty? (sre-sequence (cdr sre)))
               (error "invalid sre: empty *?" sre))
              (else
               (letrec
                   ((body
                     (lp (sre-sequence (cdr sre))
                         n
                         flags
                         (lambda (cnk init src str i end matches fail)
                           (next cnk init src str i end matches
                                 (lambda ()
                                   (body cnk init src str i end matches fail)
                                   ))))))
                 (lambda (cnk init src str i end matches fail)
                   (next cnk init src str i end matches
                         (lambda ()
                           (body cnk init src str i end matches fail))))))))
            ((+)
             (cond
              ((sre-empty? (sre-sequence (cdr sre)))
               (error "invalid sre: empty +" sre))
              (else
               (letrec
                   ((body
                     (lp (sre-sequence (cdr sre))
                         n
                         flags
                         (lambda (cnk init src str i end matches fail)
                           (body cnk init src str i end matches
                                 (lambda ()
                                   (next cnk init src str i end matches fail)
                                   ))))))
                 body))))
            ((=)
             (rec `(** ,(cadr sre) ,(cadr sre) ,@(cddr sre))))
            ((>=)
             (rec `(** ,(cadr sre) #f ,@(cddr sre))))
            ((**)
             (cond
              ((or (and (number? (cadr sre))
                        (number? (caddr sre))
                        (> (cadr sre) (caddr sre)))
                   (and (not (cadr sre)) (caddr sre)))
               (lambda (cnk init src str i end matches fail) (fail)))
              (else
               (letrec
                   ((from (cadr sre))
                    (to (caddr sre))
                    (body-contents (sre-sequence (cdddr sre)))
                    (body
                     (lambda (count)
                       (lp body-contents
                           n
                           flags
                           (lambda (cnk init src str i end matches fail)
                             (if (and to (= count to))
                                 (next cnk init src str i end matches fail)
                                 ((body (+ 1 count))
                                  cnk init src str i end matches
                                  (lambda ()
                                    (if (>= count from)
                                        (next cnk init src str i end matches fail)
                                        (fail))))))))))
                 (if (and (zero? from) to (zero? to))
                     next
                     (lambda (cnk init src str i end matches fail)
                       ((body 1) cnk init src str i end matches
                        (lambda ()
                          (if (zero? from)
                              (next cnk init src str i end matches fail)
                              (fail))))))))))
            ((**?)
             (cond
              ((or (and (number? (cadr sre))
                        (number? (caddr sre))
                        (> (cadr sre) (caddr sre)))
                   (and (not (cadr sre)) (caddr sre)))
               (lambda (cnk init src str i end matches fail) (fail)))
              (else
               (letrec
                   ((from (cadr sre))
                    (to (caddr sre))
                    (body-contents (sre-sequence (cdddr sre)))
                    (body
                     (lambda (count)
                       (lp body-contents
                           n
                           flags
                           (lambda (cnk init src str i end matches fail)
                             (if (< count from)
                                 ((body (+ 1 count)) cnk init
                                  src str i end matches fail)
                                 (next cnk init src str i end matches
                                       (lambda ()
                                         (if (and to (= count to))
                                             (fail)
                                             ((body (+ 1 count)) cnk init
                                              src str i end matches fail))))))))))
                 (if (and (zero? from) to (zero? to))
                     next
                     (lambda (cnk init src str i end matches fail)
                       (if (zero? from)
                           (next cnk init src str i end matches
                                 (lambda ()
                                   ((body 1) cnk init src str i end matches fail)))
                           ((body 1) cnk init src str i end matches fail))))))))
            ((word)
             (rec `(seq bow ,@(cdr sre) eow)))
            ((word+)
             (rec `(seq bow (+ (& (or alphanumeric "_")
                                  (or ,@(cdr sre)))) eow)))
            ((posix-string)
             (rec (string->sre (cadr sre))))
            ((look-ahead)
             (let ((check
                    (lp (sre-sequence (cdr sre))
                        n
                        flags
                        (lambda (cnk init src str i end matches fail) i))))
               (lambda (cnk init src str i end matches fail)
                 (if (check cnk init src str i end matches (lambda () #f))
                     (next cnk init src str i end matches fail)
                     (fail)))))
            ((neg-look-ahead)
             (let ((check
                    (lp (sre-sequence (cdr sre))
                        n
                        flags
                        (lambda (cnk init src str i end matches fail) i))))
               (lambda (cnk init src str i end matches fail)
                 (if (check cnk init src str i end matches (lambda () #f))
                     (fail)
                     (next cnk init src str i end matches fail)))))
            ((look-behind neg-look-behind)
             (let ((check
                    (lp (sre-sequence
                         (cons '(* any) (append (cdr sre) '(eos))))
                        n
                        flags
                        (lambda (cnk init src str i end matches fail) i))))
               (lambda (cnk init src str i end matches fail)
                 (let* ((cnk* (wrap-end-chunker cnk src i))
                        (str* ((chunker-get-str cnk*) (car init)))
                        (i* (cdr init))
                        (end* ((chunker-get-end cnk*) (car init))))
                   (if ((if (eq? (car sre) 'look-behind) (lambda (x) x) not)
                        (check cnk* init (car init) str* i* end* matches
                               (lambda () #f)))
                       (next cnk init src str i end matches fail)
                       (fail))))))
            ((atomic)
             (let ((once
                    (lp (sre-sequence (cdr sre))
                        n
                        flags
                        (lambda (cnk init src str i end matches fail) i))))
               (lambda (cnk init src str i end matches fail)
                 (let ((j (once cnk init src str i end matches (lambda () #f))))
                   (if j
                       (next cnk init src str j end matches fail)
                       (fail))))))
            ((if)
             (let* ((test-submatches (sre-count-submatches (cadr sre)))
                    (pass (lp (caddr sre) flags (+ n test-submatches) next))
                    (fail (if (pair? (cdddr sre))
                              (lp (cadddr sre)
                                  (+ n test-submatches
                                     (sre-count-submatches (caddr sre)))
                                  flags
                                  next)
                              (lambda (cnk init src str i end matches fail)
                                (fail)))))
               (cond
                ((or (number? (cadr sre)) (symbol? (cadr sre)))
                 (let ((index
                        (if (symbol? (cadr sre))
                            (cond
                             ((assq (cadr sre) names) => cdr)
                             (else
                              (error "unknown named backref in SRE IF" sre)))
                            (cadr sre))))
                   (lambda (cnk init src str i end matches fail2)
                     (if (%irregex-match-end-chunk matches index)
                         (pass cnk init src str i end matches fail2)
                         (fail cnk init src str i end matches fail2)))))
                (else
                 (let ((test (lp (cadr sre) n flags pass)))
                   (lambda (cnk init src str i end matches fail2)
                     (test cnk init src str i end matches
                           (lambda () (fail cnk init src str i end matches fail2)))
                     ))))))
            ((backref backref-ci)
             (let ((n (cond ((number? (cadr sre)) (cadr sre))
                            ((assq (cadr sre) names) => cdr)
                            (else (error "unknown backreference" (cadr sre)))))
                   (compare (if (or (eq? (car sre) 'backref-ci)
                                    (flag-set? flags ~case-insensitive?))
                                string-ci=?
                                string=?)))
               (lambda (cnk init src str i end matches fail)
                 (let ((s (irregex-match-substring matches n)))
                   (if (not s)
                       (fail)
                       ;; XXXX create an abstract subchunk-compare
                       (let lp ((src src)
                                (str str)
                                (i i)
                                (end end)
                                (j 0)
                                (len (string-length s)))
                         (cond
                          ((<= len (- end i))
                           (cond
                            ((compare (substring s j (string-length s))
                                      (substring str i (+ i len)))
                             (next cnk init src str (+ i len) end matches fail))
                            (else
                             (fail))))
                          (else
                           (cond
                            ((compare (substring s j (+ j (- end i)))
                                      (substring str i end))
                             (let ((src2 ((chunker-get-next cnk) src)))
                               (if src2
                                   (lp src2
                                       ((chunker-get-str cnk) src2)
                                       ((chunker-get-start cnk) src2)
                                       ((chunker-get-end cnk) src2)
                                       (+ j (- end i))
                                       (- len (- end i)))
                                   (fail))))
                            (else
                             (fail)))))))))))
            ((dsm)
             (lp (sre-sequence (cdddr sre)) (+ n (cadr sre)) flags next))
            (($ submatch)
             (let ((body
                    (lp (sre-sequence (cdr sre))
                        (+ n 1)
                        flags
                        (lambda (cnk init src str i end matches fail)
                          (let ((old-source
                                 (%irregex-match-end-chunk matches n))
                                (old-index
                                 (%irregex-match-end-index matches n)))
                            (irregex-match-end-chunk-set! matches n src)
                            (irregex-match-end-index-set! matches n i)
                            (next cnk init src str i end matches
                                  (lambda ()
                                    (irregex-match-end-chunk-set!
                                     matches n old-source)
                                    (irregex-match-end-index-set!
                                     matches n old-index)
                                    (fail))))))))
               (lambda (cnk init src str i end matches fail)
                 (let ((old-source (%irregex-match-start-chunk matches n))
                       (old-index (%irregex-match-start-index matches n)))
                   (irregex-match-start-chunk-set! matches n src)
                   (irregex-match-start-index-set! matches n i)
                   (body cnk init src str i end matches
                         (lambda ()
                           (irregex-match-start-chunk-set!
                            matches n old-source)
                           (irregex-match-start-index-set!
                            matches n old-index)
                           (fail)))))))
            ((=> submatch-named)
             (rec `(submatch ,@(cddr sre))))
            (else
             (error "unknown regexp operator" sre)))))
     ((symbol? sre)
      (case sre
        ((any)
         (lambda (cnk init src str i end matches fail)
           (if (< i end)
               (next cnk init src str (+ i 1) end matches fail)
               (let ((src2 ((chunker-get-next cnk) src)))
                 (if src2
                     (let ((str2 ((chunker-get-str cnk) src2))
                           (i2 ((chunker-get-start cnk) src2))
                           (end2 ((chunker-get-end cnk) src2)))
                       (next cnk init src2 str2 (+ i2 1) end2 matches fail))
                     (fail))))))
        ((nonl)
         (lambda (cnk init src str i end matches fail)
           (if (< i end)
               (if (not (eqv? #\newline (string-ref str i)))
                   (next cnk init src str (+ i 1) end matches fail)
                   (fail))
               (let ((src2 ((chunker-get-next cnk) src)))
                 (if src2
                     (let ((str2 ((chunker-get-str cnk) src2))
                           (i2 ((chunker-get-start cnk) src2))
                           (end2 ((chunker-get-end cnk) src2)))
                       (if (not (eqv? #\newline (string-ref str2 i2)))
                           (next cnk init src2 str2 (+ i2 1) end2 matches fail)
                           (fail)))
                     (fail))))))
        ((bos)
         (lambda (cnk init src str i end matches fail)
           (if (and (eq? src (car init)) (eqv? i (cdr init)))
               (next cnk init src str i end matches fail)
               (fail))))
        ((bol)
         (lambda (cnk init src str i end matches fail)
           (if (let ((ch (if (> i ((chunker-get-start cnk) src))
                             (string-ref str (- i 1))
                             (chunker-prev-char cnk init src))))
                 (or (not ch) (eqv? #\newline ch)))
               (next cnk init src str i end matches fail)
               (fail))))
        ((bow)
         (lambda (cnk init src str i end matches fail)
           (if (and (if (> i ((chunker-get-start cnk) src))
                        (not (char-alphanumeric? (string-ref str (- i 1))))
                        (let ((ch (chunker-prev-char cnk init src)))
                          (or (not ch) (not (char-alphanumeric? ch)))))
                    (if (< i end)
                        (char-alphanumeric? (string-ref str i))
                        (let ((next ((chunker-get-next cnk) src)))
                          (and next
                               (char-alphanumeric?
                                (string-ref ((chunker-get-str cnk) next)
                                            ((chunker-get-start cnk) next)))))))
               (next cnk init src str i end matches fail)
               (fail))))
        ((eos)
         (lambda (cnk init src str i end matches fail)
           (if (and (>= i end) (not ((chunker-get-next cnk) src)))
               (next cnk init src str i end matches fail)
               (fail))))
        ((eol)
         (lambda (cnk init src str i end matches fail)
           (if (if (< i end)
                   (eqv? #\newline (string-ref str i))
                   (let ((src2 ((chunker-get-next cnk) src)))
                     (if (not src2)
                         #t
                         (eqv? #\newline
                               (string-ref ((chunker-get-str cnk) src2)
                                           ((chunker-get-start cnk) src2))))))
               (next cnk init src str i end matches fail)
               (fail))))
        ((eow)
         (lambda (cnk init src str i end matches fail)
           (if (and (if (< i end)
                        (not (char-alphanumeric? (string-ref str i)))
                        (let ((ch (chunker-next-char cnk src)))
                          (or (not ch) (not (char-alphanumeric? ch)))))
                    (if (> i ((chunker-get-start cnk) src))
                        (char-alphanumeric? (string-ref str (- i 1)))
                        (let ((prev (chunker-prev-char cnk init src)))
                          (or (not prev) (char-alphanumeric? prev)))))
               (next cnk init src str i end matches fail)
               (fail))))
        ((nwb)  ;; non-word-boundary
         (lambda (cnk init src str i end matches fail)
           (let ((c1 (if (< i end)
                         (string-ref str i)
                         (chunker-next-char cnk src)))
                 (c2 (if (> i ((chunker-get-start cnk) src))
                         (string-ref str (- i 1))
                         (chunker-prev-char cnk init src))))
             (if (and c1 c2
                      (if (char-alphanumeric? c1)
                          (char-alphanumeric? c2)
                          (not (char-alphanumeric? c2))))
                 (next cnk init src str i end matches fail)
                 (fail)))))
        ((epsilon)
         next)
        (else
         (let ((cell (assq sre sre-named-definitions)))
           (if cell
               (rec (cdr cell))
               (error "unknown regexp" sre))))))
     ((char? sre)
      (if (flag-set? flags ~case-insensitive?)
          ;; case-insensitive
          (lambda (cnk init src str i end matches fail)
            (if (>= i end)
                (let lp ((src2 ((chunker-get-next cnk) src)))
                  (if src2
                      (let ((str2 ((chunker-get-str cnk) src2))
                            (i2 ((chunker-get-start cnk) src2))
                            (end2 ((chunker-get-end cnk) src2)))
                        (if (>= i2 end2)
                            (lp ((chunker-get-next cnk) src2))
                            (if (char-ci=? sre (string-ref str2 i2))
                                (next cnk init src2 str2 (+ i2 1) end2
                                      matches fail)
                                (fail))))
                      (fail)))
                (if (char-ci=? sre (string-ref str i))
                    (next cnk init src str (+ i 1) end matches fail)
                    (fail))))
          ;; case-sensitive
          (lambda (cnk init src str i end matches fail)
            (if (>= i end)
                (let lp ((src2 ((chunker-get-next cnk) src)))
                  (if src2
                      (let ((str2 ((chunker-get-str cnk) src2))
                            (i2 ((chunker-get-start cnk) src2))
                            (end2 ((chunker-get-end cnk) src2)))
                        (if (>= i2 end2)
                            (lp ((chunker-get-next cnk) src2))
                            (if (char=? sre (string-ref str2 i2))
                                (next cnk init src2 str2 (+ i2 1) end2
                                      matches fail)
                                (fail))))
                      (fail)))
                (if (char=? sre (string-ref str i))
                    (next cnk init src str (+ i 1) end matches fail)
                    (fail))))
          ))
     ((string? sre)
      (rec (sre-sequence (string->list sre)))
;; XXXX reintroduce faster string matching on chunks
;;       (if (flag-set? flags ~case-insensitive?)
;;           (rec (sre-sequence (string->list sre)))
;;           (let ((len (string-length sre)))
;;             (lambda (cnk init src str i end matches fail)
;;               (if (and (<= (+ i len) end)
;;                        (%substring=? sre str 0 i len))
;;                   (next str (+ i len) matches fail)
;;                   (fail)))))
      )
     (else
      (error "unknown regexp" sre)))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Character Sets
;;
;; Simple character sets as lists of ranges, as used in the NFA/DFA
;; compilation.  This is not especially efficient, but is portable and
;; scalable for any range of character sets.

(define (sre-cset->procedure cset next)
  (lambda (cnk init src str i end matches fail)
    (if (< i end)
        (if (cset-contains? cset (string-ref str i))
            (next cnk init src str (+ i 1) end matches fail)
            (fail))
        (let ((src2 ((chunker-get-next cnk) src)))
          (if src2
              (let ((str2 ((chunker-get-str cnk) src2))
                    (i2 ((chunker-get-start cnk) src2))
                    (end2 ((chunker-get-end cnk) src2)))
                (if (cset-contains? cset (string-ref str2 i2))
                    (next cnk init src2 str2 (+ i2 1) end2 matches fail)
                    (fail)))
              (fail))))))

(define (make-cset) (vector))
(define (range->cset from to) (vector (cons from to)))
(define (char->cset ch) (vector (cons ch ch)))
(define (cset-empty? cs) (zero? (vector-length cs)))
(define (maybe-cset->char cs)
  (if (and (= (vector-length cs) 1)
           (char=? (car (vector-ref cs 0)) (cdr (vector-ref cs 0))))
      (car (vector-ref cs 0))
      cs))

;; Since csets are sorted, there's only one possible representation of any cset
(define cset=? equal?)

(define (cset-size cs)
  (let ((len (vector-length cs)))
   (let lp ((i 0) (size 0))
     (if (= i len)
         size
         (lp (+ i 1) (+ size 1
                        (- (char->integer (cdr (vector-ref cs i)))
                           (char->integer (car (vector-ref cs i))))))))))

(define (cset->plist cs)
  (let lp ((i (- (vector-length cs) 1))
           (res '()))
    (if (= i -1)
        res
        (lp (- i 1) (cons (car (vector-ref cs i))
                          (cons (cdr (vector-ref cs i)) res))))))

(define (plist->cset ls)
  (let lp ((ls ls) (res (make-cset)))
    (if (null? ls)
        res
        (lp (cddr ls) (cset-union (range->cset (car ls) (cadr ls)) res)))))

(define (string->cset s)
  (fold (lambda (ch cs)
          (cset-adjoin cs ch))
        (make-cset)
        (string->list s)))

(define (sre->cset sre . o)
  (let lp ((sre sre) (ci? (and (pair? o) (car o))))
    (define (rec sre) (lp sre ci?))
    (cond
     ((pair? sre)
      (if (string? (car sre))
          (if ci?
              (cset-case-insensitive (string->cset (car sre)))
              (string->cset (car sre)))
          (case (car sre)
            ((~)
             (cset-complement
              (fold cset-union (rec (cadr sre)) (map rec (cddr sre)))))
            ((&)
             (fold cset-intersection (rec (cadr sre)) (map rec (cddr sre))))
            ((-)
             (fold (lambda (x res) (cset-difference res x))
                   (rec (cadr sre))
                   (map rec (cddr sre))))
            ((/)
             (let ((res (plist->cset (sre-flatten-ranges (cdr sre)))))
               (if ci?
                   (cset-case-insensitive res)
                   res)))
            ((or)
             (fold cset-union (rec (cadr sre)) (map rec (cddr sre))))
            ((w/case)
             (lp (sre-alternate (cdr sre)) #f))
            ((w/nocase)
             (lp (sre-alternate (cdr sre)) #t))
            (else
             (error "not a valid sre char-set operator" sre)))))
     ((char? sre) (if ci?
                      (cset-case-insensitive (range->cset sre sre))
                      (range->cset sre sre)))
     ((string? sre) (rec (list sre)))
     (else
      (let ((cell (assq sre sre-named-definitions)))
        (if cell
            (rec (cdr cell))
            (error "not a valid sre char-set" sre)))))))

(define (cset->sre cset)
  (cons '/
        (fold (lambda (x res) (cons (car x) (cons (cdr x) res)))
              '()
              (vector->list cset))))

(define (cset-contains? cset ch)
  (let ((len (vector-length cset)))
    (case len
      ((0) #f)
      ((1) (let ((range (vector-ref cset 0)))
             (and (char<=? ch (cdr range)) (char<=? (car range) ch))))
      (else (let lp ((lower 0) (upper len))
              (let* ((middle (quotient (+ upper lower) 2))
                     (range (vector-ref cset middle)))
                (cond ((char<? (cdr range) ch)
                       (let ((next (+ middle 1)))
                         (and (< next upper) (lp next upper))))
                      ((char<? ch (car range))
                       (and (< lower middle) (lp lower middle)))
                      (else #t))))))))

(define (char-ranges-union a b)
  (cons (if (char<=? (car a) (car b)) (car a) (car b))
        (if (char>=? (cdr a) (cdr b)) (cdr a) (cdr b))))

(define (cset-union a b)
  (let union-range ((a (vector->list a))
                    (b (vector->list b))
                    (res '()))
    (cond
     ((null? a) (list->vector (reverse (append (reverse b) res))))
     ((null? b) (list->vector (reverse (append (reverse a) res))))
     (else
      (let ((a-range (car a))
            (b-range (car b)))
        (cond
         ;; Can't use next-char here since it will cause an error if we are
         ;; comparing a cset with the maximum character as high char.
         ((< (+ (char->integer (cdr a-range)) 1) (char->integer (car b-range)))
          (union-range (cdr a) b (cons a-range res)))
         ((> (char->integer (car a-range)) (+ (char->integer (cdr b-range)) 1))
          (union-range (cdr b) a (cons b-range res)))
         ((char>=? (cdr a-range) (car b-range))
          (union-range (cons (char-ranges-union a-range b-range) (cdr a))
                       (cdr b)
                       res))
         (else (union-range (cdr a)
                            (cons (char-ranges-union a-range b-range) (cdr b))
                            res))))))))

(define (cset-adjoin cs ch) (cset-union cs (char->cset ch)))

(define (next-char c)
  (integer->char (+ (char->integer c) 1)))

(define (prev-char c)
  (integer->char (- (char->integer c) 1)))

(define (cset-difference a b)
  (let diff ((a (vector->list a))
             (b (vector->list b))
             (res '()))
    (cond ((null? a) (list->vector (reverse res)))
          ((null? b) (list->vector (append (reverse res) a)))
          (else
           (let ((a-range (car a))
                 (b-range (car b)))
             (cond
              ((char<? (cdr a-range) (car b-range))
               (diff (cdr a) b (cons a-range res)))
              ((char>? (car a-range) (cdr b-range))
               (diff a (cdr b) res))
              ((and (char<=? (car b-range) (car a-range))
                    (char>=? (cdr b-range) (cdr a-range)))
               (diff (cdr a) b res))
              (else (let ((left (and (char<? (car a-range) (car b-range))
                                     (cons (car a-range)
                                           (prev-char (car b-range)))))
                          (right (and (char>? (cdr a-range) (cdr b-range))
                                      (cons (next-char (cdr b-range))
                                            (cdr a-range)))))
                      (diff (if right (cons right (cdr a)) (cdr a))
                            b
                            (if left (cons left res) res))))))))))

(define (min-char a b)
  (if (char<? a b) a b))

(define (max-char a b)
  (if (char<? a b) b a))

(define (cset-intersection a b)
  (let intersect ((a (vector->list a))
                  (b (vector->list b))
                  (res '()))
    (if (or (null? a) (null? b))
        (list->vector (reverse res))
        (let ((a-range (car a))
              (b-range (car b)))
          (cond
           ((char<? (cdr a-range) (car b-range))
            (intersect (cdr a) b res))
           ((char>? (car a-range) (cdr b-range))
            (intersect a (cdr b) res))
           (else
            (let ((result (cons (max-char (car b-range) (car a-range))
                                (min-char (cdr a-range) (cdr b-range)))))
              (intersect (if (char>? (cdr a-range) (cdr result))
                             a (cdr a))
                         (if (char>? (cdr b-range) (cdr result))
                             b (cdr b))
                         (cons result res)))))))))

(define (cset-complement a)
  (cset-difference (sre->cset *all-chars*) a))

;; This could use some optimization :)
(define (cset-case-insensitive a)
  (let lp ((ls (vector->list a)) (res '()))
    (cond ((null? ls) (list->vector (reverse res)))
          ((and (char-alphabetic? (caar ls))
                (char-alphabetic? (cdar ls)))
           (lp (cdr ls)
               (reverse
                (vector->list
                 (cset-union (cset-union (list->vector (reverse res))
                                         (vector (car ls)))
                             (range->cset (char-altcase (caar ls))
                                          (char-altcase (cdar ls))))))))
          (else (lp (cdr ls) (reverse (vector->list
                                       (cset-union (list->vector (reverse res))
                                                   (vector (car ls))))))))))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;;; Match and Replace Utilities

(define (irregex-fold/fast irx kons knil str . o)
  (if (not (string? str)) (error "irregex-fold: not a string" str))
  (let* ((irx (irregex irx))
         (matches (irregex-new-matches irx))
         (finish (or (and (pair? o) (car o)) (lambda (i acc) acc)))
         (start (if (and (pair? o) (pair? (cdr o))) (cadr o) 0))
         (end (if (and (pair? o) (pair? (cdr o)) (pair? (cddr o)))
                  (caddr o)
                  (string-length str)))
         (init-src (list str start end))
         (init (cons init-src start)))
    (if (not (and (integer? start) (exact? start)))
        (error "irregex-fold: not an exact integer" start))
    (if (not (and (integer? end) (exact? end)))
        (error "irregex-fold: not an exact integer" end))
    (irregex-match-chunker-set! matches irregex-basic-string-chunker)
    (let lp ((src init-src) (from start) (i start) (acc knil))
      (if (>= i end)
          (finish from acc)
          (let ((m (irregex-search/matches
                    irx
                    irregex-basic-string-chunker
                    init
                    src
                    i
                    matches)))
            (if (not m)
                (finish from acc)
                (let ((j-start (%irregex-match-start-index m 0))
                      (j (%irregex-match-end-index m 0))
                      (acc (kons from m acc)))
                  (irregex-reset-matches! matches)
                  (cond
                   ((flag-set? (irregex-flags irx) ~consumer?)
                    (finish j acc))
                   ((= j j-start)
                    ;; skip one char forward if we match the empty string
                    (lp (list str j end) j (+ j 1) acc))
                   (else
                    (lp (list str j end) j j acc))))))))))

(define (irregex-fold irx kons . args)
  (if (not (procedure? kons)) (error "irregex-fold: not a procedure" kons))
  (let ((kons2 (lambda (i m acc) (kons i (irregex-copy-matches m) acc))))
    (apply irregex-fold/fast irx kons2 args)))

(define (irregex-fold/chunked/fast irx kons knil cnk start . o)
  (let* ((irx (irregex irx))
         (matches (irregex-new-matches irx))
         (finish (or (and (pair? o) (car o)) (lambda (src i acc) acc)))
         (i (if (and (pair? o) (pair? (cdr o)))
                (cadr o)
                ((chunker-get-start cnk) start)))
         (init (cons start i)))
    (if (not (integer? i)) (error "irregex-fold/chunked: not an integer" i))
    (irregex-match-chunker-set! matches cnk)
    (let lp ((start start) (i i) (acc knil))
      (if (not start)
          (finish start i acc)
          (let ((m (irregex-search/matches irx cnk init start i matches)))
            (if (not m)
                (finish start i acc)
                (let ((end-src (%irregex-match-end-chunk m 0))
                      (end-index (%irregex-match-end-index m 0)))
                  (if (and (eq? end-src start) (= end-index i))
                      (if (>= end-index ((chunker-get-end cnk) end-src ))
                          (let ((next ((chunker-get-next cnk) end-src)))
                            (lp next ((chunker-get-start cnk) next) acc))
                          (lp end-src (+ end-index 1) acc))
                      (let ((acc (kons start i m acc)))
                        (irregex-reset-matches! matches)
                        (if (flag-set? (irregex-flags irx) ~consumer?)
                            (finish end-src end-index acc)
                            (lp end-src end-index acc)))))))))))

(define (irregex-fold/chunked irx kons . args)
  (if (not (procedure? kons)) (error "irregex-fold/chunked: not a procedure" kons))
  (let ((kons2 (lambda (s i m acc) (kons s i (irregex-copy-matches m) acc))))
    (apply irregex-fold/chunked/fast irx kons2 args)))

(define (irregex-replace irx str . o)
  (if (not (string? str)) (error "irregex-replace: not a string" str))
  (let ((m (irregex-search irx str)))
    (if m
        (string-cat-reverse
         (cons (substring str (%irregex-match-end-index m 0) (string-length str))
               (append (irregex-apply-match m o)
                       (list (substring str 0 (%irregex-match-start-index m 0)))
                       )))
        str)))

(define (irregex-replace/all irx str . o)
  (if (not (string? str)) (error "irregex-replace/all: not a string" str))
  (irregex-fold/fast
   irx
   (lambda (i m acc)
     (let ((m-start (%irregex-match-start-index m 0)))
       (if (>= i m-start)
           (append (irregex-apply-match m o) acc)
           (append (irregex-apply-match m o)
                   (cons (substring str i m-start) acc)))))
   '()
   str
   (lambda (i acc)
     (let ((end (string-length str)))
       (string-cat-reverse (if (>= i end)
                               acc
                               (cons (substring str i end) acc)))))))

(define (irregex-apply-match m ls)
  (let lp ((ls ls) (res '()))
    (if (null? ls)
        res
        (cond
         ((integer? (car ls))
          (lp (cdr ls)
              (cons (or (irregex-match-substring m (car ls)) "") res)))
         ((procedure? (car ls))
          (lp (cdr ls) (cons ((car ls) m) res)))
         ((symbol? (car ls))
          (case (car ls)
            ((pre)
             (lp (cdr ls)
                 (cons (substring (car (%irregex-match-start-chunk m 0))
                                  0
                                  (%irregex-match-start-index m 0))
                       res)))
            ((post)
             (let ((str (car (%irregex-match-start-chunk m 0))))
               (lp (cdr ls)
                   (cons (substring str
                                    (%irregex-match-end-index m 0)
                                    (string-length str))
                         res))))
            (else
             (cond
              ((assq (car ls) (irregex-match-names m))
               => (lambda (x) (lp (cons (cdr x) (cdr ls)) res)))
              (else
               (error "unknown match replacement" (car ls)))))))
         (else
          (lp (cdr ls) (cons (car ls) res)))))))

(define (irregex-extract irx str . o)
  (if (not (string? str)) (error "irregex-extract: not a string" str))
  (apply irregex-fold/fast
         irx
         (lambda (i m a) (cons (irregex-match-substring m) a))
         '()
         str
         (lambda (i a) (reverse a))
         o))

(define (irregex-split irx str . o)
  (if (not (string? str)) (error "irregex-split: not a string" str))
  (let ((start (if (pair? o) (car o) 0))
        (end (if (and (pair? o) (pair? (cdr o))) (cadr o) (string-length str))))
    (irregex-fold/fast
     irx
     (lambda (i m a)
       (cond
        ((= i (%irregex-match-start-index m 0))
         a)
        (else
         (cons (substring str i (%irregex-match-start-index m 0)) a))))
     '()
     str
     (lambda (i a)
       (let lp ((ls (if (= i end) a (cons (substring str i end) a)))
                (res '())
                (was-char? #f))
         (cond
          ((null? ls) res)
          ((char? (car ls))
           (lp (cdr ls)
               (if (or was-char? (null? res))
                   (cons (string (car ls)) res)
                   (cons (string-append (string (car ls)) (car res))
                         (cdr res)))
               #t))
          (else (lp (cdr ls) (cons (car ls) res) #f)))))
     start
     end)))