John Cowan <cowan@mercury.ccil.org> wrote:

> Jean-Michel HUFFLEN scripsit:
>
> (...)
>
>> Now, if we open an output port with the Latin-1 encoding, some valid
>> characters of Unicode cannot be written: what happens in such a case?
>
> It's implementation-dependent.

    I understand your point of view, but here is the problem I point out.

    In Scheme, a well-known of implementation-dependent feature is the
order for evaluating the arguments of a function. You may write dirty
code such that:

(- (read) (read))

that may result in what you expect on a particular interpreter. But
obviously this code is not portable. On another point, we can write
portable code, even if we do not know the order for evaluating
arguments. That is why I think that this feature is not bad; for me,
portability is very important, I developed a large application which
runs on several Scheme interpreters/compilers.

    If we consider now (open-input-file ...) R5RS did not provide a
standard function to check if the input file exists, and we were
unable to catch the error signalled. The only solution was a kind of
plug-and-socket mechanism to use nonstandard functions like
"file-exists?" provided by most of Scheme interpreters. This
implementation-dependent feature was bad from my point of view, since
we have to search particular implementations for nonstandard functions.

    Let us go back to characters. You do not want to give any
priviledge to a particular encoding. OK. How can I write portable
code, running on several interpreters? Some characters may be not
included in the encoding used for writing characters. How can I make
sure that I will avoid errors? For me, if I had:
    - a function returning the default encoding used,
    - a function returning the available encodings,
I would be the happiest programmer. Encodings and error management
would be implementation-dependent, but we would have a way to get
information about what a particular implementation can provide. You
mentioned that Java and C# do not provide such functions. I would be
unhappy if I have to program my applications in Java or C#.

    Cheers,

J.-M. Hufflen

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