[gambit-list] Returning a symbol to scheme from C
Alex Young
alex at blackkettle.org
Tue Feb 19 05:42:50 EST 2013
On 18/02/2013 17:39, Jeff Read wrote:
>
> On Feb 18, 2013 11:21 AM, "Alex Young" <alex at blackkettle.org
> <mailto:alex at blackkettle.org>> wrote:
>
> > I've got a C function behind a c-lambda which needs to do some grubbing
> > around with a select(2) call and decide on a scheme symbol to return as
> > an indication of what it did, and whether an error condition occurred.
> > Basically I want to use that symbol as a signal to drive a transition in
> > a state machine.
> >
> > How one gets hold of a named symbol as a ___SCMOBJ (or anything more
> > appropriate) from C isn't explained in the docs, and the wiki seems to
> > have fallen over. It's also not immediately obvious from gambit.h
> > whether there's a macro for this purpose.
> >
>
> I think there are a couple of ways you can do this:
>
> 1) c-define a Scheme procedure that returns the symbols you're
> interested in based on some parameter. In the most general case it could
> be just a wrapper around string->symbol.
I had thought of that. I was rather hoping there'd be something a
little cleaner though. I'll give it a try, though - it's worth
benchmarking to see if it's going to cause problems.
> 2) you're returning symbols so I think you want your C function to
> return to Scheme. Have your C function return a result code and wrap it
> in a Scheme procedure that maps the result code onto a symbol. You can
> look at Gamsock on the dumping ground for examples of how to wrap a
> low-level C function in a Scheme procedure that handles the Scheme objects.
>
Yeah, I was trying to avoid having to do this. I'd be defining the
return codes twice - once as ints (or whatever) and once as symbols. I
guess that's all macroable away, but still... not particularly elegant.
Thanks for the suggestions :-)
--
Alex
More information about the Gambit-list
mailing list