ikarus/scheme/ikarus.io.input-strings.ss

92 lines
3.0 KiB
Scheme

(library (ikarus io input-strings)
(export open-input-string with-input-from-string)
(import
(ikarus system $strings)
(ikarus system $bytevectors)
(ikarus system $fx)
(ikarus system $pairs)
(ikarus system $ports)
(ikarus system $io)
(except (ikarus) open-input-string with-input-from-string))
(define-syntax message-case
(syntax-rules (else)
[(_ msg args
[(msg-name msg-arg* ...) b b* ...] ...
[else else1 else2 ...])
(let ([tmsg msg] [targs args])
(define-syntax match-and-bind
(syntax-rules ()
[(__ y () body)
(if (null? y)
body
(error 'message-case "unmatched ~s" (cons tmsg targs)))]
[(__ y (a a* (... ...)) body)
(if (pair? y)
(let ([a (car y)] [d (cdr y)])
(match-and-bind d (a* (... ...)) body))
(error 'message-case "unmatched ~s" (cons tmsg targs)))]))
(case tmsg
[(msg-name)
(match-and-bind targs (msg-arg* ...) (begin b b* ...))] ...
[else else1 else2 ...]))]))
(define make-input-string-handler
(lambda (str)
(let ((open? #t) (idx 0) (n (string-length str)))
(lambda (msg . args)
(message-case msg args
[(read-char p)
(if ($fx< idx n)
(let ([c ($string-ref str idx)])
(set! idx ($fxadd1 idx))
c)
(if open?
(eof-object)
(error 'read-char "port ~s is closed" p)))]
[(peek-char p)
(if ($fx< idx n)
($string-ref str idx)
(if open?
(eof-object)
(error 'peek-char "port ~s is closed" p)))]
[(unread-char c p)
(let ([i ($fxsub1 idx)])
(if (and ($fx>= i 0)
($fx< i n))
(set! idx i)
(if open?
(error 'unread-char "port ~s is closed" p)
(error 'unread-char "too many unread-chars"))))]
[(port-name p) '*string-port*]
[(close-port p)
(when open?
(set! open? #f))]
[else
(error 'input-string-handler
"message not handled ~s" (cons msg args))])))))
(define open-input-string
(lambda (str)
(unless (string? str)
(error 'open-input-string "~s is not a string" str))
(let ([port (make-input-port
(make-input-string-handler str)
'#vu8())])
port)))
(define with-input-from-string
(lambda (str proc)
(unless (string? str)
(error 'with-input-from-string "~s is not a string" str))
(unless (procedure? proc)
(error 'with-input-from-string "~s is not a procedure" proc))
(let ([p (open-input-string str)])
(parameterize ([current-input-port p])
(proc)))))
)