Re: g-wrap <gw-guile-wct> questions

[Steve Tell]

On Mon, 16 Aug 2004, Andy Wingo wrote:

> Hey Steve,
> 
> On Mon, 16 Aug 2004, Steve Tell wrote:
> 
> > (define-method (wrap-value-cg (wct <gw:parport*>)
> >                               (value <gw-value>)
> >                               status-var)
> >   (let ((wct-var (slot-ref wct 'wct-var-name))
> >         (sv (scm-var value))
> >         (cv (var value)))
> >     (list
> >      "if(" cv " == NULL) scm_syserror_msg(\"wrap(gw:parport*)\", \"error 
> > ~a\", SCM_EOL, errno);\n"
> >      "else " sv " = gw_wcp_assimilate_ptr((void *) " cv ", " wct-var 
> > ");\n")))
> > 
> > 
> > (I'm doing the call to scm_syserror_msg wrong somehow; 
> 
> Yeah, you should be using gw:error. It's a bizarre construct, e.g.
> 
>         `(gw:error ,status-var type ,(wrapped-var value))
> 
> First the gw:error symbol, then the name of the status var, then a
> symbol indicating which kind of error, then type-specific args:
> 
> ;; (list 'gw:error status-var 'misc msg format-args)
> ;; (list 'gw:error status-var 'memory)
> ;; (list 'gw:error status-var 'range scm-item-out-of-range)
> ;; (list 'gw:error status-var 'type scm-bad-type-item)
> ;; (list 'gw:error status-var 'argc)


Thanks for clearing that up; it is a bit tangled.  
(I'm curious why GWerror and gw:error are necessary; it can't be for
portability to non-guile targets since the wrap/unwrap methods are
already in the guile-specific side of g-wrap.)

Anyway, I'm back in town and fooling with this again.

A gw:error of flavor 'misc seems to be what I want, but I can't seem to
get the format-args to work.  Here's somthing that I think ought to be close:


define-method (wrap-value-cg (wct <gw:parport*>)
                              (value <gw-value>)
                              status-var)
  (let ((wct-var (slot-ref wct 'wct-var-name))
        (sv (scm-var value))
        (cv (var value)))
    (list
     "if(" cv " == NULL)\n"
     `(gw:error ,status-var misc "\"syserror ~S\"" 
"scm_cons(scm_strerror(SCM_MAKINUM(errno)),SCM_EOL)")
     "else " sv " = gw_wcp_assimilate_ptr((void *) " cv ", " wct-var ");\n")))


When my testbench causes an error to check all this, I get:

test-guile-dev-parport.scm:73:14: In procedure parport-open-device in 
expression (parport-open-device "/dev/barfport0bad"):
test-guile-dev-parport.scm:73:14: syserror ~S

The message string is printed, but not interpreted by format together with the
arguments.

My current workaround is to change the gw:error line to this:
 `(gw:error ,status-var misc "strerror(errno)" "scm_cons(SCM_BOOL_F,SCM_EOL)")

which produces an acceptable message:

test-guile-dev-parport.scm:73:14: In procedure parport-open-device in 
expression (parport-open-device "/dev/barfport0bad"):
test-guile-dev-parport.scm:73:14: No such file or directory


Following things down into guile-1.6.4/libguile, I think this is safe
- the static message from strerror appears to get copied into a
guile-string soon enough - but I feel like the format-message with
args ought to work.  It would be necessary for other more interesting cases. 

Steve