Re: [PATCH] Fix `get-string-n!' &i/o-decoding exception behavior

[Mark H Weaver <mhw@netris.org>]

Andreas Rottmann <a.rottmann@gmx.at> writes:

> Mark H Weaver <mhw@netris.org> writes:
>
>> Why not leave the API as-is, and in the event of an error, just raise
>> the proper R6RS exception from within 'scm_get_string_n_x'?
>>
> The problem here is that we have no easy way to raise R6RS exceptions
> from C code, AFAICT.  It is certainly possible, but if it involves
> convoluted code of doing imports of condition types and appropriate
> constructors, then constructing a proper invocation, all in C, I'd
> rather avoid it.

It's not that bad.  In Guile 2.0 we have some convenient procedures for
accessing arbitrary Scheme variables from C.

Looking at your patch, I see that if '%get-string-n!' returned an error,
then you did:

  (raise (make-i/o-decoding-error port))

This can be written in C as follows:

  scm_call_1 (scm_c_public_ref ("rnrs exceptions", "raise"),
              scm_call_1 (scm_c_public_ref ("rnrs io ports",
                                            "make-i/o-decoding-error")));

Alternatively, you could write one or more private helper procedures in
Scheme to raise R6RS exceptions, and call those private helpers from C
using 'scm_c_private_ref' instead of 'scm_c_public_ref'.

What do you think?

   Regards,
     Mark