GNU bug report logs - #24816
Bug in (rnrs io ports) procedure open-string-output-port

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Freja Nordsiek <fnordsie <at> gmail.com>
To: bug-guile <at> gnu.org
Subject: Bug in (rnrs io ports) procedure open-string-output-port
Date: Sat, 29 Oct 2016 17:29:09 +0700

The "open-string-output-port" procedure in (rnrs io ports) returns two
values, a string port and a thunk that returns a string of the
characters written to the port so far. In the R6RS standard documents,
the reading procedure is destructive, in that it clears all the
characters written to the port so far (though, it does not close it,
so it can still be used). However, in Guile 2.1.4, the characters are
not cleared and so running the thunk again immediately afterwards will
produce the same output, which is a bug.

This can be tested running the following script


    (import (rnrs base (6))
            (rnrs io ports (6))
            (rnrs io simple (6)))

    (let-values (((p get-output) (open-string-output-port)))
      (display "hello" p)
      (flush-output-port p)
      (let ((out-first (get-output)))
        (let ((out-second (get-output)))
          (display (string-append "Follows R6RS: "
                                  (if (string=? out-first out-second)
                                      "no"
                                      "yes")))
          (newline)
          (display (string-append "out-first: " out-first))
          (newline)
          (display (string-append "out-second: " out-second))
          (newline))))


which produces the following output in guile


    Follows R6RS: no
    out-first: hello
    out-second: hello


when it should output



    Follows R6RS: yes
    out-first: hello
    out-second:


instead.




Freja Nordsiek

Message #10 received at 24816-done <at> debbugs.gnu.org (full text, mbox):

From: Andy Wingo <wingo <at> pobox.com>
To: Freja Nordsiek <fnordsie <at> gmail.com>
Cc: 24816-done <at> debbugs.gnu.org
Subject: Re: bug#24816: Bug in (rnrs io ports) procedure
 open-string-output-port
Date: Wed, 01 Mar 2017 14:26:50 +0100

On Sat 29 Oct 2016 12:29, Freja Nordsiek <fnordsie <at> gmail.com> writes:

> The "open-string-output-port" procedure in (rnrs io ports) returns two
> values, a string port and a thunk that returns a string of the
> characters written to the port so far. In the R6RS standard documents,
> the reading procedure is destructive, in that it clears all the
> characters written to the port so far (though, it does not close it,
> so it can still be used). However, in Guile 2.1.4, the characters are
> not cleared and so running the thunk again immediately afterwards will
> produce the same output, which is a bug.

Thanks for the report; fixed in git.  Cheers :)

Andy

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