doco C error handling

[Kevin Ryde]

        * scheme-control.texi (Handling Errors): Revise C support section to
        get index entries and clarify parameters.  Remove scm_regex_error, no
        longer exists and wasn't available to applications.

I hope I'm right that scm_regex_error is gone, it doesn't show up in a
grep.

Incidentally, is the regex-error error key described in the scheme
section of this node be regular-expression-syntax, as per the
`make-regexp' doco?


Revised text:

C Support
---------

In the following C functions, SUBR and MESSAGE parameters can be `NULL'
to give the `#f' described above.

 - Function: SCM scm_error (SCM key, char *subr, char *message, SCM
          args, SCM rest)
     Throw an error, as per `scm-error' above.

 - Function: void scm_syserror (char *subr)
 - Function: void scm_syserror_msg (char *subr, char *message, SCM args)
     Throw an error with key `system-error' and supply `errno' in the
     REST argument.  For `scm_syserror' the message is generated using
     `strerror'.

     Of course care should be taken that any code in between the failing
     operation and the call to these routines doesn't change `errno'.

 - Function: void scm_num_overflow (char *subr)
 - Function: void scm_out_of_range (char *subr, SCM bad_value)
 - Function: void scm_wrong_num_args (SCM proc)
 - Function: void scm_wrong_type_arg (char *subr, int pos, SCM
          bad_value)
 - Function: void scm_memory_error (char *subr)
     Throw an error with the various keys described above.

     For `scm_wrong_num_args', PROC should be a Scheme symbol which is
     the name of the procedure incorrectly invoked.

   Exception handlers can also be installed from C, using
`scm_internal_catch', `scm_lazy_catch', or `scm_stack_catch' from
`libguile/throw.c'.  These have not yet been documented, but the source
contains some useful comments.

scheme-control.texi.c-errors.diff
Description: Text document