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184 lines
8.3 KiB
Racket
184 lines
8.3 KiB
Racket
#lang racket/base
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(require "util.rkt" syntax/id-table racket/syntax)
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(provide parse)
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(define (bad-args stx num)
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(raise-syntax-error #f (format "incorrect number of arguments (should have ~a)" num) stx))
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;; char-range-arg: syntax-object syntax-object -> nat
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;; If c contains is a character or length 1 string, returns the integer
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;; for the character. Otherwise raises a syntax error.
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(define (char-range-arg stx containing-stx)
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(define c (syntax-e stx))
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(cond
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[(char? c) (char->integer c)]
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[(and (string? c) (= (string-length c) 1))
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(char->integer (string-ref c 0))]
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[else
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(raise-syntax-error
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#f
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"not a char or single-char string"
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containing-stx stx)]))
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(module+ test
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(check-equal? (char-range-arg #'#\1 #'here) (char->integer #\1))
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(check-equal? (char-range-arg #'"1" #'here) (char->integer #\1)))
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(define orig-insp (variable-reference->module-declaration-inspector
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(#%variable-reference)))
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(define (disarm stx)
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(syntax-disarm stx orig-insp))
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;; parse : syntax-object (box (list-of syntax-object)) -> s-re (see re.rkt)
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;; checks for errors and generates the plain s-exp form for s
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;; Expands lex-abbrevs and applies lex-trans.
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(define (parse stx)
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(let loop ([stx stx]
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;; seen-lex-abbrevs: id-table
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[seen-lex-abbrevs (make-immutable-free-id-table)])
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(let ([recur (λ (s)
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(loop (syntax-rearm s stx)
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seen-lex-abbrevs))]
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[recur/abbrev (λ (s id)
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(loop (syntax-rearm s stx)
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(free-id-table-set seen-lex-abbrevs id id)))])
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(syntax-case (disarm stx) (repetition union intersection complement concatenation
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char-range char-complement)
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[_
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(identifier? stx)
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(let ([expansion (syntax-local-value/record stx (λ (v) #t))])
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(unless (lex-abbrev? expansion)
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(raise-syntax-error 'regular-expression
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"undefined abbreviation"
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stx))
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;; Check for cycles.
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(when (free-id-table-ref seen-lex-abbrevs stx (λ () #f))
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(raise-syntax-error 'regular-expression
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"illegal lex-abbrev cycle detected"
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stx
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#f
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(list (free-id-table-ref seen-lex-abbrevs stx))))
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(recur/abbrev ((lex-abbrev-get-abbrev expansion)) stx))]
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[_
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(or (char? (syntax-e stx)) (string? (syntax-e stx)))
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(syntax-e stx)]
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[(repetition ARG ...)
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(let ([arg-list (syntax->list #'(ARG ...))])
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(unless (= 3 (length arg-list))
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(bad-args stx 2))
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(define low (syntax-e (car arg-list)))
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(define high (syntax-e (cadr arg-list)))
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(define re (caddr arg-list))
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(unless (and (number? low) (exact? low) (integer? low) (>= low 0))
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(raise-syntax-error #f "not a non-negative exact integer" stx (car arg-list)))
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(unless (or (and (number? high) (exact? high) (integer? high) (>= high 0))
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(eqv? high +inf.0))
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(raise-syntax-error #f "not a non-negative exact integer or +inf.0" stx (cadr arg-list)))
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(unless (<= low high)
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(raise-syntax-error #f "the first argument is not less than or equal to the second argument" stx))
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`(repetition ,low ,high ,(recur re)))]
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[(union RE ...)
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`(union ,@(map recur (syntax->list #'(RE ...))))]
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[(intersection RE ...)
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`(intersection ,@(map recur (syntax->list #'(RE ...))))]
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[(complement RE ...)
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(let ([re-list (syntax->list #'(RE ...))])
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(unless (= 1 (length re-list))
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(bad-args stx 1))
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`(complement ,(recur (car re-list))))]
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[(concatenation RE ...)
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`(concatenation ,@(map recur (syntax->list #'(RE ...))))]
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[(char-range ARG ...)
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(let ((arg-list (syntax->list #'(ARG ...))))
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(unless (= 2 (length arg-list))
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(bad-args stx 2))
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(let ([i1 (char-range-arg (car arg-list) stx)]
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[i2 (char-range-arg (cadr arg-list) stx)])
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(if (<= i1 i2)
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`(char-range ,(integer->char i1) ,(integer->char i2))
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(raise-syntax-error #f "the first argument does not precede or equal second argument" stx))))]
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[(char-complement ARG ...)
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(let ([arg-list (syntax->list #'(ARG ...))])
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(unless (= 1 (length arg-list))
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(bad-args stx 1))
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(define parsed (recur (car arg-list)))
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(unless (char-set? parsed)
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(raise-syntax-error #f "not a character set" stx (car arg-list)))
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`(char-complement ,parsed))]
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((OP form ...)
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(identifier? #'OP)
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(let* ([expansion (syntax-local-value/record #'OP (λ (v) #t))])
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(cond
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[(lex-trans? expansion)
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(recur ((lex-trans-f expansion) (disarm stx)))]
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[expansion
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(raise-syntax-error 'regular-expression "not a lex-trans" stx)]
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[else
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(raise-syntax-error 'regular-expression "undefined operator" stx)])))
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[_ (raise-syntax-error 'regular-expression "not a char, string, identifier, or (op args ...)" stx)]))))
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;; char-set? : s-re -> bool
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;; A char-set is an re that matches only strings of length 1.
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;; char-set? is conservative.
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(define (char-set? s-re)
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(cond
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[(char? s-re)]
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[(string? s-re) (= (string-length s-re) 1)]
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[(list? s-re) (case (car s-re)
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[(union intersection) (andmap char-set? (cdr s-re))]
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[(char-range char-complement) #t]
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[(repetition) (and (= 1 (cadr s-re) (caddr s-re)) (char-set? (cadddr s-re)))]
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[(concatenation) (and (= 2 (length s-re)) (char-set? (cadr s-re)))]
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(else #f))]
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[else #f]))
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(module+ test
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(require rackunit)
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(check-equal? (char-set? #\a) #t)
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(check-equal? (char-set? "12") #f)
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(check-equal? (char-set? "1") #t)
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(check-equal? (char-set? '(repetition 1 2 #\1)) #f)
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(check-equal? (char-set? '(repetition 1 1 "12")) #f)
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(check-equal? (char-set? '(repetition 1 1 "1")) #t)
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(check-equal? (char-set? '(repetition 6 6 "1")) #f)
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(check-equal? (char-set? '(union "1" "2" "3")) #t)
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(check-equal? (char-set? '(union "1" "" "3")) #f)
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(check-equal? (char-set? '(intersection "1" "2" (union "3" "4"))) #t)
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(check-equal? (char-set? '(intersection "1" "")) #f)
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(check-equal? (char-set? '(complement "1")) #f)
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(check-equal? (char-set? '(concatenation "1" "2")) #f)
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(check-equal? (char-set? '(concatenation "" "2")) #f)
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(check-equal? (char-set? '(concatenation "1")) #t)
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(check-equal? (char-set? '(concatenation "12")) #f)
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(check-equal? (char-set? '(char-range #\1 #\2)) #t)
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(check-equal? (char-set? '(char-complement #\1)) #t))
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;; yikes... these test cases all have the wrong arity, now.
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;; and by "now", I mean it's been broken since before we
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;; moved to git.
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(module+ test
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(check-equal? (parse #'#\a) #\a)
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(check-equal? (parse #'"1") "1")
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(check-equal? (parse #'(repetition 1 1 #\1))
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'(repetition 1 1 #\1))
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(check-equal? (parse #'(repetition 0 +inf.0 #\1)) '(repetition 0 +inf.0 #\1))
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(check-equal? (parse #'(union #\1 (union "2") (union)))
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'(union #\1 (union "2") (union)))
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(check-equal? (parse #'(intersection #\1 (intersection "2") (intersection)))
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'(intersection #\1 (intersection "2") (intersection)))
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(check-equal? (parse #'(complement (union #\1 #\2)))
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'(complement (union #\1 #\2)))
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(check-equal? (parse #'(concatenation "1" "2" (concatenation)))
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'(concatenation "1" "2" (concatenation)))
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(check-equal? (parse #'(char-range "1" #\1)) '(char-range #\1 #\1))
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(check-equal? (parse #'(char-range #\1 "1")) '(char-range #\1 #\1))
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(check-equal? (parse #'(char-range "1" "3")) '(char-range #\1 #\3))
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(check-equal? (parse #'(char-complement (union "1" "2")))
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'(char-complement (union "1" "2")))
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(check-equal? (parse #'(char-complement (repetition 1 1 "1")))
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'(char-complement (repetition 1 1 "1")))
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(check-exn #rx"not a character set"
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(λ () (parse #'(char-complement (repetition 6 6 "1"))))))
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