Programming Praxis

; pregexp.ss

; http://ds26gte.github.io/pregexp/index.html
; https://github.com/ds26gte/pregexp
; https://github.com/ds26gte/pregexp/blob/master/pregexp.scm

;pregexp.scm
;Portable regular expressions for Scheme
;Dorai Sitaram
;http://www.ccs.neu.edu/~dorai
;dorai AT ccs DOT neu DOT edu
;Oct 2, 1999

(define *pregexp-version* 20050502) ;last change

(define *pregexp-comment-char* #\;)

(define *pregexp-nul-char-int*
  ;can't assume #\nul maps to 0 because of Scsh
  (- (char->integer #\a) 97))

(define *pregexp-return-char*
  ;can't use #\return because it isn't R5RS
  (integer->char
    (+ 13 *pregexp-nul-char-int*)))

(define *pregexp-tab-char*
  ;can't use #\tab because it isn't R5RS
  (integer->char
    (+ 9 *pregexp-nul-char-int*)))

(define *pregexp-space-sensitive?* #t)

(define pregexp-reverse!
  ;the useful reverse! isn't R5RS
  (lambda (s)
    (let loop ((s s) (r '()))
      (if (null? s) r
          (let ((d (cdr s)))
            (set-cdr! s r)
            (loop d s))))))

(define pregexp-error
  ;R5RS won't give me a portable error procedure.
  ;modify this as needed
  (lambda whatever 
    (display "Error:")
    (for-each (lambda (x) (display #\space) (write x))
              whatever)
    (newline)
    (error 'pregexp "pregexp-error")))

(define pregexp-read-pattern
  (lambda (s i n)
    (if (>= i n)
        (list
          (list ':or (list ':seq)) i)
        (let loop ((branches '()) (i i))
          (if (or (>= i n)
                  (char=? (string-ref s i) #\)))
              (list (cons ':or (pregexp-reverse! branches)) i)
              (let ((vv (pregexp-read-branch
                          s
                          (if (char=? (string-ref s i) #\|) (+ i 1) i) n)))
                (loop (cons (car vv) branches) (cadr vv))))))))

(define pregexp-read-branch
  (lambda (s i n)
    (let loop ((pieces '()) (i i))
      (cond ((>= i n)
             (list (cons ':seq (pregexp-reverse! pieces)) i))
            ((let ((c (string-ref s i)))
               (or (char=? c #\|)
                   (char=? c #\))))
             (list (cons ':seq (pregexp-reverse! pieces)) i))
            (else (let ((vv (pregexp-read-piece s i n)))
                    (loop (cons (car vv) pieces) (cadr vv))))))))

(define pregexp-read-piece
  (lambda (s i n)
    (let ((c (string-ref s i)))
      (case c
        ((#\^) (list ':bos (+ i 1)))
        ((#\$) (list ':eos (+ i 1)))
        ((#\.) (pregexp-wrap-quantifier-if-any
                 (list ':any (+ i 1)) s n))
        ((#\[) (let ((i+1 (+ i 1)))
                 (pregexp-wrap-quantifier-if-any
                   (case (and (
                  (lambda (num-i)
                    (list (list ':backref (car num-i)) (cadr num-i))))
                 ((pregexp-read-escaped-char s i n) =>
                  (lambda (char-i)
                    (list (car char-i) (cadr char-i))))
                 (else (pregexp-error 'pregexp-read-piece 'backslash)))
           s n))
        (else
          (if (or *pregexp-space-sensitive?*
                  (and (not (char-whitespace? c))
                       (not (char=? c *pregexp-comment-char*))))
              (pregexp-wrap-quantifier-if-any
                (list c (+ i 1)) s n)
              (let loop ((i i) (in-comment? #f))
                (if (>= i n) (list ':empty i)
                    (let ((c (string-ref s i)))
                      (cond (in-comment?
                              (loop (+ i 1)
                                (not (char=? c #\newline))))
                            ((char-whitespace? c)
                             (loop (+ i 1) #f))
                            ((char=? c *pregexp-comment-char*)
                             (loop (+ i 1) #t))
                            (else (list ':empty i))))))))))))

(define pregexp-read-escaped-number
  (lambda (s i n)
    ; s[i] = \
    (and (= i n)
                      (list (string->number
                              (list->string (pregexp-reverse! r))) i)
                      (let ((c (string-ref s i)))
                        (if (char-numeric? c)
                            (loop (+ i 1) (cons c r))
                            (list (string->number
                                    (list->string (pregexp-reverse! r)))
                              i))))))))))

(define pregexp-read-escaped-char
  (lambda (s i n)
    ; s[i] = \
    (and (= i n)
            (pregexp-error 'pregexp-read-posix-char-class)
            (let ((c (string-ref s i)))
              (cond ((char=? c #\^)
                     (set! neg? #t)
                     (loop (+ i 1) r))
                    ((char-alphabetic? c)
                     (loop (+ i 1) (cons c r)))
                    ((char=? c #\:)
                     (if (or (>= (+ i 1) n)
                             (not (char=? (string-ref s (+ i 1)) #\])))
                         (pregexp-error 'pregexp-read-posix-char-class)
                         (let ((posix-class
                                 (string->symbol
                                   (list->string (pregexp-reverse! r)))))
                           (list (if neg? (list ':neg-char posix-class)
                                     posix-class)
                             (+ i 2)))))
                    (else
                      (pregexp-error
                        'pregexp-read-posix-char-class)))))))))

(define pregexp-read-cluster-type
  (lambda (s i n)
    ; s[i-1] = left-paren
    (let ((c (string-ref s i)))
      (case c
        ((#\?)
         (let ((i (+ i 1)))
           (case (string-ref s i)
             ((#\:) (list '() (+ i 1)))
             ((#\=) (list '(:lookahead) (+ i 1)))
             ((#\!) (list '(:neg-lookahead) (+ i 1)))
             ((#\>) (list '(:no-backtrack) (+ i 1)))
             ((#\= i n)
                             (begin (set-car! (cdr new-re) #f)
                               (set-car! (cdr new-vv) i))
                             (let ((c (string-ref s i)))
                               (cond ((and (char-whitespace? c)
                                           (not *pregexp-space-sensitive?*))
                                      (loop (+ i 1)))
                                     ((char=? c #\?)
                                      (set-car! (cdr new-re) #t)
                                      (set-car! (cdr new-vv) (+ i 1)))
                                     (else (set-car! (cdr new-re) #f)
                                       (set-car! (cdr new-vv) i))))))
                       new-vv))
                    (else vv)))))))))

;

(define pregexp-read-nums
  (lambda (s i n)
    ; s[i-1] = {
    ; returns (p q k) where s[k] = }
    (let loop ((p '()) (q '()) (k i) (reading 1))
      (if (>= k n) (pregexp-error 'pregexp-read-nums))
      (let ((c (string-ref s k)))
        (cond ((char-numeric? c)
               (if (= reading 1)
                   (loop (cons c p) q (+ k 1) 1)
                   (loop p (cons c q) (+ k 1) 2)))
              ((and (char-whitespace? c) (not *pregexp-space-sensitive?*))
               (loop p q (+ k 1) reading))
              ((and (char=? c #\,) (= reading 1))
               (loop p q (+ k 1) 2))
              ((char=? c #\})
               (let ((p (string->number
                          (list->string (pregexp-reverse! p))))
                     (q (string->number
                          (list->string (pregexp-reverse! q)))))
                 (cond ((and (not p) (= reading 1)) (list 0 #f k))
                       ((= reading 1) (list p p k))
                       (else (list p q k)))))
              (else #f))))))

(define pregexp-invert-char-list
  (lambda (vv)
    (set-car! (car vv) ':none-of-chars)
    vv))

;

(define pregexp-read-char-list
  (lambda (s i n)
    (let loop ((r '()) (i i))
      (if (>= i n)
          (pregexp-error 'pregexp-read-char-list
                         'character-class-ended-too-soon)
          (let ((c (string-ref s i)))
            (case c
              ((#\]) (if (null? r)
                         (loop (cons c r) (+ i 1))
                         (list (cons ':one-of-chars (pregexp-reverse! r)) 
                               (+ i 1))))
              ((#\\ )
               (let ((char-i (pregexp-read-escaped-char s i n)))
                 (if char-i (loop (cons (car char-i) r) (cadr char-i))
                     (pregexp-error 'pregexp-read-char-list 'backslash))))
              ((#\-) (if (or (null? r)
                             (let ((i+1 (+ i 1)))
                               (and ( n1 n) (fk)
          (let loop ((j 0) (k i))
            (cond ((>= j n1) (sk k))
                  ((>= k n) (fk))
                  ((char=? (string-ref s1 j) (string-ref s k))
                   (loop (+ j 1) (+ k 1)))
                  (else (fk))))))))

(define pregexp-char-word?
  (lambda (c)
    ;too restrictive for Scheme but this
    ;is what \w is in most regexp notations
    (or (char-alphabetic? c)
        (char-numeric? c)
        (char=? c #\_))))

(define pregexp-at-word-boundary?
  (lambda (s i n)
    (or (= i 0) (>= i n)
        (let ((c/i (string-ref s i))
              (c/i-1 (string-ref s (- i 1))))
          (let ((c/i/w? (pregexp-check-if-in-char-class?
                          c/i ':word))
                (c/i-1/w? (pregexp-check-if-in-char-class?
                            c/i-1 ':word)))
            (or (and c/i/w? (not c/i-1/w?))
                (and (not c/i/w?) c/i-1/w?)))))))

(define pregexp-check-if-in-char-class?
  (lambda (c char-class)
    (case char-class
      ((:any) (not (char=? c #\newline)))
      ;
      ((:alnum) (or (char-alphabetic? c) (char-numeric? c)))
      ((:alpha) (char-alphabetic? c))
      ((:ascii) (integer c) 128))
      ((:blank) (or (char=? c #\space) (char=? c *pregexp-tab-char*)))
      ((:cntrl) (integer c) 32))
      ((:digit) (char-numeric? c))
      ((:graph) (and (>= (char->integer c) 32)
                     (not (char-whitespace? c))))
      ((:lower) (char-lower-case? c))
      ((:print) (>= (char->integer c) 32))
      ((:punct) (and (>= (char->integer c) 32)
                     (not (char-whitespace? c))
                     (not (char-alphabetic? c))
                     (not (char-numeric? c))))
      ((:space) (char-whitespace? c))
      ((:upper) (char-upper-case? c))
      ((:word) (or (char-alphabetic? c)
                   (char-numeric? c)
                   (char=? c #\_)))
      ((:xdigit) (or (char-numeric? c)
                     (char-ci=? c #\a) (char-ci=? c #\b)
                     (char-ci=? c #\c) (char-ci=? c #\d)
                     (char-ci=? c #\e) (char-ci=? c #\f)))
      (else (pregexp-error 'pregexp-check-if-in-char-class?)))))

(define pregexp-list-ref
  (lambda (s i)
    ;like list-ref but returns #f if index is
    ;out of bounds
    (let loop ((s s) (k 0))
      (cond ((null? s) #f)
            ((= k i) (car s))
            (else (loop (cdr s) (+ k 1)))))))

;re is a compiled regexp.  It's a list that can't be
;nil.  pregexp-match-positions-aux returns a 2-elt list whose
;car is the string-index following the matched
;portion and whose cadr contains the submatches.
;The proc returns false if there's no match.

;Am spelling loop- as loup- because these shouldn't
;be translated into CL loops by scm2cl (although
;they are tail-recursive in Scheme)

(define pregexp-make-backref-list
  (lambda (re)
    (let sub ((re re))
      (if (pair? re)
          (let ((car-re (car re))
                (sub-cdr-re (sub (cdr re))))
            (if (eqv? car-re ':sub) 
                (cons (cons re #f) sub-cdr-re)
                (append (sub car-re) sub-cdr-re)))
          '()))))

(define pregexp-match-positions-aux
  (lambda (re s sn start n i)
    (let ((identity (lambda (x) x))
          (backrefs (pregexp-make-backref-list re))
          (case-sensitive? #t))
      (let sub ((re re) (i i) (sk identity) (fk (lambda () #f)))
        ;(printf "sub ~s ~s\n" i re)
        (cond ((eqv? re ':bos)
               ;(if (= i 0) (sk i) (fk))
               (if (= i start) (sk i) (fk))
               )
              ((eqv? re ':eos)
               ;(if (>= i sn) (sk i) (fk))
               (if (>= i n) (sk i) (fk))
               )
              ((eqv? re ':empty)
               (sk i))
              ((eqv? re ':wbdry)
               (if (pregexp-at-word-boundary? s i n)
                   (sk i)
                   (fk)))
              ((eqv? re ':not-wbdry)
               (if (pregexp-at-word-boundary? s i n)
                   (fk)
                   (sk i)))
              ((and (char? re) (< i n))
               ;(printf "bingo\n")
               (if ((if case-sensitive? char=? char-ci=?)
                    (string-ref s i) re)
                   (sk (+ i 1)) (fk)))
              ((and (not (pair? re)) (< i n))
               (if (pregexp-check-if-in-char-class?
                     (string-ref s i) re)
                   (sk (+ i 1)) (fk)))
              ((and (pair? re) (eqv? (car re) ':char-range) (< i n))
               (let ((c (string-ref s i)))
                 (if (let ((c< (if case-sensitive? char<=? char-ci<=?)))
                       (and (c= i n) (fk)
                      (let loup-one-of-chars ((chars (cdr re)))
                        (if (null? chars) (fk)
                            (sub (car chars) i sk
                                 (lambda ()
                                   (loup-one-of-chars (cdr chars))))))))
                 ((:neg-char)
                  (if (>= i n) (fk)
                      (sub (cadr re) i 
                           (lambda (i1) (fk))
                           (lambda () (sk (+ i 1))))))
                 ((:seq)
                  (let loup-seq ((res (cdr re)) (i i))
                    (if (null? res) (sk i )
                        (sub (car res) i 
                             (lambda (i1 )
                               (loup-seq (cdr res) i1 ))
                             fk))))
                 ((:or)
                  (let loup-or ((res (cdr re)))
                    (if (null? res) (fk)
                        (sub (car res) i 
                             (lambda (i1 )
                               (or (sk i1 )
                                   (loup-or (cdr res))))
                             (lambda () (loup-or (cdr res)))))))
                 ((:backref)
                  (let* ((c (pregexp-list-ref backrefs (cadr re)))
                         (backref
                           (cond (c => cdr)
                                 (else 
                                   (pregexp-error
                                     'pregexp-match-positions-aux
                                     'non-existent-backref re)
                                   #f))))
                    (if backref
                        (pregexp-string-match
                          (substring s (car backref) (cdr backref))
                          s i n (lambda (i) (sk i)) fk)
                        (sk i))))
                 ((:sub)
                  (sub (cadr re) i 
                       (lambda (i1)
                         (set-cdr! (assv re backrefs) (cons i i1))
                         (sk i1)) fk))
                 ((:lookahead)
                  (let ((found-it?
                          (sub (cadr re) i
                               identity (lambda () #f))))
                    (if found-it? (sk i) (fk))))
                 ((:neg-lookahead)
                  (let ((found-it?
                          (sub (cadr re) i
                               identity (lambda () #f))))
                    (if found-it? (fk) (sk i))))
                 ((:lookbehind)
                  (let ((n-actual n) (sn-actual sn)) 
                    (set! n i) (set! sn i)
                    (let ((found-it?
                            (sub (list ':seq '(:between #f 0 #f :any)
                                       (cadr re) ':eos) 0 
                                 identity (lambda () #f))))
                      (set! n n-actual) (set! sn sn-actual)
                      (if found-it? (sk i) (fk)))))
                 ((:neg-lookbehind)
                  (let ((n-actual n) (sn-actual sn)) 
                    (set! n i) (set! sn i)
                    (let ((found-it?
                            (sub (list ':seq '(:between #f 0 #f :any)
                                       (cadr re) ':eos) 0
                                 identity (lambda () #f))))
                      (set! n n-actual) (set! sn sn-actual)
                      (if found-it? (fk) (sk i)))))
                 ((:no-backtrack)
                  (let ((found-it? (sub (cadr re) i
                                        identity (lambda () #f))))
                    (if found-it?
                        (sk found-it?) 
                        (fk))))
                 ((:case-sensitive :case-insensitive)
                  (let ((old case-sensitive?))
                    (set! case-sensitive?
                      (eqv? (car re) ':case-sensitive))
                    (sub (cadr re) i 
                         (lambda (i1)
                           (set! case-sensitive? old)
                           (sk i1))
                         (lambda ()
                           (set! case-sensitive? old)
                           (fk)))))
                 ((:between)
                  (let* ((maximal? (not (cadr re)))
                         (p (caddr re)) 
                         (q (cadddr re))
                         (could-loop-infinitely? (and maximal? (not q)))
                         (re (car (cddddr re))))
                    (let loup-p ((k 0) (i i) )
                      (if (= k q)) (fk)
                                    (if maximal?
                                        (sub re i
                                             (lambda (i1)
                                               (if (and could-loop-infinitely?
                                                        (= i1 i))
                                                   (pregexp-error
                                                     'pregexp-match-positions-aux
                                                     'greedy-quantifier-operand-could-be-empty))
                                               (or (loup-q (+ k 1) i1)
                                                   (fk)))
                                             fk)
                                        (or (fk)
                                            (sub re i 
                                                 (lambda (i1)
                                                   (loup-q (+ k 1) i1))
                                                 fk)))))))))))
                 (else (pregexp-error 'pregexp-match-positions-aux))))
              ((>= i n) (fk))
              (else (pregexp-error 'pregexp-match-positions-aux))))
      ;(printf "done\n")
      (let ((backrefs (map cdr backrefs)))
        (and (car backrefs) backrefs)))))

(define pregexp-replace-aux
  (lambda (str ins n backrefs)
    (let loop ((i 0) (r ""))
      (if (>= i n) r
          (let ((c (string-ref ins i)))
            (if (char=? c #\\ )
                (let* ((br-i (pregexp-read-escaped-number ins i n))
                       (br (if br-i (car br-i)
                               (if (char=? (string-ref ins (+ i 1)) #\&) 0
                                   #f)))
                       (i (if br-i (cadr br-i)
                              (if br (+ i 2)
                                  (+ i 1)))))
                  (if (not br)
                      (let ((c2 (string-ref ins i)))
                        (loop (+ i 1)
                          (if (char=? c2 #\$) r
                              (string-append r (string c2)))))
                      (loop i
                        (let ((backref (pregexp-list-ref backrefs br)))
                          (if backref
                              (string-append r
                                (substring str (car backref)
                                           (cdr backref)))
                              r)))))
                (loop (+ i 1) (string-append r (string c)))))))))

(define pregexp
  (lambda (s)
    (set! *pregexp-space-sensitive?* #t) ;in case it got corrupted
    (list ':sub (car (pregexp-read-pattern s 0 (string-length s))))))

(define pregexp-match-positions
  (lambda (pat str . opt-args)
    (cond ((string? pat) (set! pat (pregexp pat)))
          ((pair? pat) #t)
          (else (pregexp-error 'pregexp-match-positions 
                               'pattern-must-be-compiled-or-string-regexp
                               pat)))
    (let* ((str-len (string-length str))
           (start (if (null? opt-args) 0
                      (let ((start (car opt-args)))
                        (set! opt-args (cdr opt-args))
                        start)))
           (end (if (null? opt-args) str-len 
                    (car opt-args))))
      (let loop ((i start))
        (and (= i n) (pregexp-reverse! r))
              ((pregexp-match-positions pat str i n)
               =>
               (lambda (y)
                 (let ((jk (car y)))
                   (let ((j (car jk)) (k (cdr jk)))
                     ;(printf "j = ~a; k = ~a; i = ~a~n" j k i)
                     (cond ((= j k)
                            ;(printf "producing ~s~n"
                            ; (substring str i (+ j 1)))
                            (loop (+ k 1) 
                                  (cons (substring str i (+ j 1)) r) #t))
                           ((and (= j i) picked-up-one-undelimited-char?)
                            (loop k r #f))
                           (else
                             ;(printf "producing ~s~n" (substring str i j))
                             (loop k (cons (substring str i j) r) #f)))))))
              (else (loop n (cons (substring str i n) r) #f)))))))

(define pregexp-replace
  (lambda (pat str ins)
    (let* ((n (string-length str))
           (pp (pregexp-match-positions pat str 0 n)))
      (if (not pp) str
          (let ((ins-len (string-length ins))
                (m-i (caar pp))
                (m-n (cdar pp)))
            (string-append
              (substring str 0 m-i)
              (pregexp-replace-aux str ins ins-len pp)
              (substring str m-n n)))))))

(define pregexp-replace*
  (lambda (pat str ins)
    ;return str with every occurrence of pat 
    ;replaced by ins
    (let ((pat (if (string? pat) (pregexp pat) pat))
          (n (string-length str))
          (ins-len (string-length ins)))
      (let loop ((i 0) (r ""))
        ;i = index in str to start replacing from
        ;r = already calculated prefix of answer 
        (if (>= i n) r 
            (let ((pp (pregexp-match-positions pat str i n)))
              (if (not pp) 
                  (if (= i 0)
                      ;this implies pat didn't match str at
                      ;all, so let's return original str
                      str
                      ;else: all matches already found and
                      ;replaced in r, so let's just
                      ;append the rest of str
                      (string-append
                       r (substring str i n)))
                  (loop (cdar pp)
                        (string-append
                         r
                         (substring str i (caar pp))
                         (pregexp-replace-aux str ins ins-len pp))))))))))

(define pregexp-quote
  (lambda (s)
    (let loop ((i (- (string-length s) 1)) (r '()))
      (if (string r)
          (loop (- i 1)
                (let ((c (string-ref s i)))
                  (if (memv c '(#\\ #\. #\? #\* #\+ #\| #\^ #\$
                                    #\[ #\] #\{ #\} #\( #\)))
                      (cons #\\ (cons c r))
                      (cons c r))))))))
    

;(trace pregexp-read-pattern pregexp-read-char-list pregexp-read-piece)
;eof

Pages: 1 2 3 4 5 6 7 8 9 10