/usr/lib/s9fes/regex.scm is in scheme9 2010.11.13-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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; By Nils M Holm, 2009,2010
; See the LICENSE file of the S9fES package for terms of use
;
; (re-comp string) ==> list
; (re-match list string) ==> list | #f
; (re-match list string 'symbol ...) ==> list | #f
; (re-subst list string1 string2) ==> list | #f
; (re-subst list string1 string2 'symbol) ==> list | #f
;
; (load-from-library "regex.scm")
;
; Compile, match, and substitute regular expressions.
;
; RE-COMP compiles a regular expression (RE) and returns it.
; Compiled REs (CREs) are represented by lists.
;
; RE-MATCH matches a compiled RE against a string. When (part of) the
; string matches the CRE, it returns a list of the form
;
; ((first limit) ...)
;
; where FIRST is the index of the first character matching the RE and
; LIMIT is the first character *after* the match (so the match can be
; extracted with SUBSTRING). When no submatches are used, just a list
; of the form ((first limit)) will be returned. When submatches using
; \( and \) are contained in the regular expression, the subsequent pairs
; will contain the ranges matched by the sub-expressions (in order of
; occurrence of sub-expressions in the RE). See examples.
;
; When the CRE does not match the string, RE-MATCH returns #F.
;
; A special case occurs when a given pattern may match a string of zero
; length. In this case, RE-MATCH returns () when no better match could
; be found.
;
; When 'LAZY is passed as an additional argument to RE-MATCH, it matches
; repetitions "lazily," e.g.: "A+" will match "A" (rather than "AAA")
; in "AAAB".
;
; When 'ALL is passed as an additional argument to RE-MATCH, it will
; generate a list of *all* matches found in the given string, i.e. a
; list of the form:
;
; (((first limit) ...) ...)
;
; The following RE patterns are evaluated:
; . match any character
; [char...] match character class (may contain ranges of the form c1-c2)
; ^ match beginning of line
; $ match end of line
; * match zero or more instances of the preceding pattern
; + match one or more instances of the preceding pattern
; ? match the preceding pattern optionally
; \ match the following character literally (exception below!)
; \( mark the beginning of a submatch
; \) mark the end of a submatch
;
; RE-SUBST attempts to match the CRE LIST against STRING1. When it
; succeeds, it returns a fresh copy of STRING1 with the match replaced
; by STRING2. When the 'ALL option is used (see RE-MATCH), all occurrences
; of the match will be replaced. When the CRE contains submatches, they can
; be referred to in STRING2 by using a backslash and the position of the
; submatch, i.e.: \1, \2, ... The notation \0 denotes the entire match. To
; include a literal backslash in the replacement string, use \\. (Of course,
; Scheme strings use backslashes for escaping, so you will have to use \\1
; in the place of \1 and \\\\ in the place of \\. Yes, this is awkward.)
; When SUBST fails to match the CRE, it returns #F.
;
; Example: (re-match (re-comp "^a[1-9]*z$") "a1289z") ==> ((0 6))
; (re-match (re-comp "a[1-9]+z") "___a123z___") ==> ((3 8))
; (re-match (re-comp "a[^1-9]+z") "a123z") ==> #f
; (re-match (re-comp "[1-9]*") "__1__") ==> ((2 3))
; (re-match (re-comp "[1-9]*") "_____") ==> ()
;
; (re-match (re-comp "f\\(.\\)\\(.\\)bar")
; "foobar") ==> ((0 6) (1 2) (2 3))
;
; (re-match (re-comp "a\\(.\\)a") "aba_aca_ada" 'all)
; ==> (((0 3) (1 2))
; ((4 7) (5 6))
; ((8 11) (9 10)))
;
; (re-subst (re-comp "\\([0-9]+\\)\\.\\([0-9]+\\)\\.")
; "_01.1._31.12._"
; "\\2/\\1"
; 'all) ==> "_1/01_12/31_"
(load-from-library "and-letstar.scm")
(define (re-comp re)
(define LP #\()
(define RP #\))
(define (make-range c0 cn cls)
(if (> c0 cn)
cls
(make-range (+ 1 c0)
cn
(cons (integer->char c0) cls))))
(define (compile-class in out cls first)
(cond ((null? in)
#f)
((char=? #\] (car in))
(list (cdr in) (cons (reverse! cls) out)))
((and first (char=? #\^ (car in)))
(compile-class (cdr in) out (list #\]) #f))
((and (not first)
(not (null? (cdr cls)))
(char=? #\- (car in))
(pair? (cdr in))
(not (char=? #\] (cadr in))))
(let ((c0 (char->integer (car cls)))
(cn (char->integer (cadr in))))
(if (< c0 cn)
(compile-class (cddr in)
out
(make-range c0 cn (cdr cls)) #f)
(compile-class (cdr in)
out
(cons #\- cls) #f))))
(else
(compile-class (cdr in)
out
(cons (car in) cls) #f))))
(let compile ((in-sub #f)
(in (string->list re))
(out '()))
(cond
((not in)
#f)
((null? in)
(if in-sub
#f
(reverse! out)))
(else
(case (car in)
((#\\)
(if (pair? (cdr in))
(if (memv (cadr in) '(#\( #\)))
(if (or (and in-sub (char=? LP (cadr in)))
(and (not in-sub) (char=? RP (cadr in))))
#f
(compile (char=? (cadr in) LP)
(cddr in)
(cons (list (cadr in)) out)))
(compile in-sub
(cddr in)
(cons (cadr in) out)))
#f))
((#\^ #\$ #\.)
(compile in-sub
(cdr in)
(cons (list (car in)) out)))
((#\* #\?)
(compile in-sub
(cdr in)
(if (null? out)
(cons (car in) out)
(cons (list (car in) (car out))
(cdr out)))))
((#\+)
(compile in-sub
(cdr in)
(if (null? out)
(cons (car in) out)
(cons (list #\* (car out)) out))))
((#\[)
(let ((class (compile-class (cdr in) out (list #\[) #t)))
(if class
(apply compile in-sub class)
#f)))
(else
(compile in-sub
(cdr in)
(cons (car in) out))))))))
(define (re-match cre s . opts)
(define lazy #f)
(define all-matches #f)
(define LP #\()
(define RP #\))
(define (match-char p c)
(cond ((char? p)
(char=? p c))
((char=? #\. (car p)))
((char=? #\[ (car p))
(memv c (cdr p)))
((char=? #\] (car p))
(not (memv c (cdr p))))
(else
#f)))
(define (extend-match m n)
(if (null? m)
(list (list n 0))
(cons (cons (+ 1 (caar m)) (cdar m)) (cdr m))))
(define (make-choices cre s m)
(if (or (null? s)
(not (match-char (cadar cre) (car s))))
(list (list s m))
(cons (list s m)
(make-choices cre (cdr s) (extend-match m 1)))))
(define (begin-submatch m)
(if (null? m)
`((0 0) (0 0))
`((,(caar m) ,(caar m)) ,(car m) ,@(cdr m))))
(define (end-submatch m)
(let ((sub (car m))
(main (cadr m)))
`((,(car sub) ,(cadr main)) ,sub ,@(cddr m))))
(define (match-cre cre s pos m)
(cond
((null? cre)
(map reverse! m))
((null? s)
(cond ((equal? cre '((#\$)))
(match-cre '() '() pos m))
((equal? cre `((,RP)))
(match-cre '() '() pos (end-submatch m)))
((and (pair? (car cre))
(char=? #\* (caar cre))
(null? (cdr cre)))
'())
(else
#f)))
((pair? (car cre))
(cond ((char=? LP (caar cre))
(match-cre (cdr cre)
s
pos
(begin-submatch m)))
((char=? RP (caar cre))
(match-cre (cdr cre)
s
pos
(end-submatch m)))
((char=? #\* (caar cre))
(match-star cre s pos m))
((char=? #\? (caar cre))
(if (match-char (cadar cre) (car s))
(match-cre (cdr cre)
(cdr s)
(+ 1 pos)
(extend-match m 1))
(match-cre (cdr cre) s pos m)))
((match-char (car cre) (car s))
(match-cre (cdr cre)
(cdr s)
(+ 1 pos)
(extend-match m 1)))
(else
#f)))
((char=? (car cre) (car s))
(match-cre (cdr cre)
(cdr s)
(+ 1 pos)
(extend-match m 1)))
(else
#f)))
(define (match-star cre s pos m)
(let try-choices ((c* (if lazy
(make-choices cre s m)
(reverse (make-choices cre s m)))))
(and (not (null? c*))
(let ((r (match-cre (cdr cre) (caar c*) pos (cadar c*))))
(or r
(try-choices (cdr c*)))))))
(define (adjust res pos)
(and res
(let ((res (map (lambda (range)
(map (lambda (x)
(+ x pos))
range))
res)))
`(,(car res) ,@(reverse! (cdr res))))))
(define (try-matches cre s pos)
(cond ((null? s)
(match-cre cre s pos '()))
(else
(let ((r (match-cre cre s pos '())))
(if (or (not r)
(null? r)
(and (pair? r)
(null? (car r))))
(try-matches cre (cdr s) (+ 1 pos))
(adjust r pos))))))
(define (collect-matches cre s pos)
(let loop ((r (try-matches cre s pos))
(m* '()))
(if (or (not r)
(null? r))
(reverse! m*)
(let ((k (cadar r)))
(loop (try-matches cre (list-tail s k) (+ k pos))
(cons r m*))))))
(if (memq 'lazy opts)
(set! lazy #t))
(if (memq 'all opts)
(set! all-matches #t))
(cond ((equal? cre '((#\^)))
(if all-matches
`(((0 0)))
`((0 0))))
((equal? cre '((#\$)))
(let ((k (string-length s)))
(if all-matches
`(((,k ,k)))
`((,k ,k)))))
((and (pair? cre)
(equal? '(#\^) (car cre)))
(let ((m (adjust (match-cre (cdr cre) (string->list s) 0 '()) 0)))
(if all-matches
(list m)
m)))
(all-matches
(collect-matches cre (string->list s) 0))
(else
(try-matches cre (string->list s) 0))))
(define (replacement-string new m*)
(letrec
((append-match
(lambda (m* i out)
(let loop ((in (string->list (list-ref m* i)))
(out out))
(if (null? in)
out
(loop (cdr in) (cons (car in) out)))))))
(let ((k (string-length new))
(n (length m*)))
(let loop ((i 0)
(out '()))
(cond ((>= i k)
(list->string (reverse! out)))
((char=? #\\ (string-ref new i))
(cond ((and-let* ((_ (< i (- k 1)))
(c (string-ref new (+ 1 i)))
(_ (char<=? #\0 c #\9))
(j (- (char->integer c)
(char->integer #\0)))
(_ (<= 0 j n)))
j)
=> (lambda (j)
(loop (+ 2 i) (append-match m* j out))))
((< i (- k 1))
(loop (+ 2 i) (cons (string-ref new (+ 1 i)) out)))
(else
(loop (+ 1 i) out))))
(else
(loop (+ 1 i) (cons (string-ref new i) out))))))))
(define re-subst
(let ((replacement-string replacement-string))
(lambda (cre old new . opts)
(and-let* ((pos** (apply re-match cre old opts))
(_ (not (null? pos**)))
(pos** (if (memq 'all opts)
pos**
(list pos**)))
(m** (map (lambda (pos*)
(map (lambda (pos)
(substring old (car pos) (cadr pos)))
pos*))
pos**)))
(let ((repl* (map (lambda (m*)
(replacement-string new m*))
m**)))
(let loop ((pos* (append '((0 0))
(map car pos**)
(list (list (string-length old)
(string-length old)))))
(repl* repl*)
(out '()))
(cond ((null? (cdr pos*))
(apply string-append (reverse! out)))
(else
(let ((s (substring old (cadar pos*) (caadr pos*)))
(r (if (null? repl*) "" (car repl*))))
(loop (cdr pos*)
(if (null? repl*) '() (cdr repl*))
(cons r (cons s out))))))))))))
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