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(module comment-reader scheme/base
(require (only-in racket/port peeking-input-port))
(provide (rename-out [*read read]
[*read-syntax read-syntax])
make-comment-readtable)
(define unsyntaxer (make-parameter 'unsyntax))
(define (*read [inp (current-input-port)])
(parameterize ([unsyntaxer (read-unsyntaxer inp)]
[current-readtable (make-comment-readtable)])
(read/recursive inp)))
(define (*read-syntax src [port (current-input-port)])
(parameterize ([unsyntaxer (read-unsyntaxer port)]
[current-readtable (make-comment-readtable)])
(read-syntax/recursive src port)))
(define (read-unsyntaxer port)
(let ([p (peeking-input-port port)])
(if (eq? (read p) '#:escape-id)
(begin (read port) (read port))
'unsyntax)))
(define (make-comment-readtable #:readtable [rt (current-readtable)])
(make-readtable rt
#\; 'terminating-macro
(case-lambda
[(char port)
(do-comment port (lambda () (read/recursive port #\@)))]
[(char port src line col pos)
(let ([v (do-comment port (lambda () (read-syntax/recursive src port #\@)))])
(let-values ([(eline ecol epos) (port-next-location port)])
(datum->syntax
#f
v
(list src line col pos (and pos epos (- epos pos))))))])))
(define (do-comment port recur)
(let loop ()
(when (equal? #\; (peek-char port))
(read-char port)
(loop)))
(when (equal? #\space (peek-char port))
(read-char port))
`(code:comment
(,(unsyntaxer)
(t
,@(append-strings
(let loop ()
(let ([c (read-char port)])
(cond
[(or (eof-object? c)
(char=? c #\newline))
null]
[(char=? c #\@)
(cons (recur) (loop))]
[else
(cons (string c)
(loop))]))))))))
(define (append-strings l)
(let loop ([l l][s null])
(cond
[(null? l) (if (null? s)
null
(preserve-space (apply string-append (reverse s))))]
[(string? (car l))
(loop (cdr l) (cons (car l) s))]
[else
(append (loop null s)
(cons
(car l)
(loop (cdr l) null)))])))
(define (preserve-space s)
(let ([m (regexp-match-positions #rx" +" s)])
(if m
(append (preserve-space (substring s 0 (caar m)))
(list `(hspace ,(- (cdar m) (caar m))))
(preserve-space (substring s (cdar m))))
(list s)))))
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