C error-returning functions and Guile exceptions

[Ludovic Courtès]

Hi,

I'd like to accommodate Scheme's functional style by wrapping
error-returning C functions into exception-raising Scheme functions.
Here's an example.  While on the C side I have this:

  /* Read at most AMOUNT bytes from FILE into BUFFER.  Return in *READ
     the amount of data actually read.  On error, return non-zero.  */
  errcode_t read_stuff (file_t *file, char *buffer, size_t amount,
                        size_t *read);

I'd like it to translate into Scheme into something along the lines of:

  (read-stuff file amount)

where (i) in the nominal case, a "buffer object" (or a string) is
returned (this corresponds to the BUFFER and READ arguments of the C
function) and (ii) in the error case, a Guile exception is raised that
corresponds to the error code returned by `read_stuff ()'.

So there are two things to do here:

  1.  Write a C function that wraps `read_stuff ()', checks the
      error code returned and calls `scm_throw ()' if necessary;

  2.  Find a way to make the BUFFER/READ pair translate into a return
      value of the Scheme function.

(1) is my main problem.  For (2), I could obviously create a `buffer'
SMOB and use it as the return value type, but maybe there's a more
elegant way to do this?

Thanks for writing G-Wrap, it really rocks compared to SWIG.  ;-)

Ludovic.