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Re: %default-port-conversion-strategy and string ports

From: Mark H Weaver
Subject: Re: %default-port-conversion-strategy and string ports
Date: Fri, 01 Jun 2012 18:40:12 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.0.92 (gnu/linux)

address@hidden (Ludovic Courtès) writes:
> Ports in Guile can be used to write characters, or bytes, or both.  In
> particular, every port (including string ports, void ports, etc.) has an
> “encoding”, which is actually only used for textual I/O.
> Conversely, an R6RS port is either textual or binary, but not both.
> IMO, one advantage of mixed text/binary ports is to allow things like this:
>   scheme@(guile-user)> (define (string->utf16 s)
>                          (let ((p (with-fluids ((%default-port-encoding 
> "UTF-16BE"))
>                                     (open-input-string s))))
>                            (get-bytevector-all p)))
>   scheme@(guile-user)> (string->utf16 "hello")
>   $4 = #vu8(0 104 0 101 0 108 0 108 0 111)
>   scheme@(guile-user)> (use-modules(rnrs bytevectors))
>   scheme@(guile-user)> (utf16->string $4)
>   $5 = "hello"

IMHO, this is a bad hack that exposes internal details of our
implementation of string ports, and whose only utility AFAIK is to
(partially) make up for our lack of a proper 'iconv' interface from
Scheme.  If we could enable this hack without compromising the
robustness of the _primary_ use case for string ports, then I would
merely frown at this leak of internal implementation details.
Unfortunately, it's worse than that.

Anyway, I suppose that we are now locked into this broken behavior, at
least for Guile 2.0.  I guess that your proposed solution (to make
SRFI-6 export alternative versions of 'open-input-string' and
'open-output-string' that always use UTF-8 for the port encoding) is the
best we can do now.

I have concerns about this solution, but I can't think of a better one,
given the unfortunate fact that our current semantics have been widely
deployed (and worse, that the above hack has been advertised on
guile-user as a way to work around our lack of 'iconv' from Scheme).


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