Geting the value of a top level scheme value from C

Geting the value of a top level scheme value from C

[Richard Shann]

Given a C string that is the name of a Scheme variable what is the call
I need to make from C to get the value?

That is, in the Scheme I have

(define foo "bar")

Then in C I want to write

SCM bar = scm_var_c_get_val ("foo");//imaginary function name

strcmp ("bar", scm_to_locale_string (bar));

etc...

Richard Shann

Re: Geting the value of a top level scheme value from C

[Thompson, David]

On Fri, Jan 24, 2014 at 11:54 AM, Richard Shann <richard@rshann.plus.com> wrote:
> Given a C string that is the name of a Scheme variable what is the call
> I need to make from C to get the value?
>
> That is, in the Scheme I have
>
> (define foo "bar")
>
> Then in C I want to write
>
> SCM bar = scm_var_c_get_val ("foo");//imaginary function name
>
> strcmp ("bar", scm_to_locale_string (bar));
>
> etc...
>
> Richard Shann

Hello Richard,

I think 'scm_public_ref' is what you want.

See the manual for further explanation and other procedures in case I
picked the wrong one. ;)

http://www.gnu.org/software/guile/manual/html_node/Accessing-Modules-from-C.html#Accessing-Modules-from-C

- Dave

Re: Geting the value of a top level scheme value from C

[Panicz Maciej Godek]

2014/1/24 Richard Shann <richard@rshann.plus.com>:
> Given a C string that is the name of a Scheme variable what is the call
> I need to make from C to get the value?
[...]

i think it is all well described here:
http://www.gnu.org/software/guile/manual/html_node/Accessing-Modules-from-C.html

however, note that according to the manual, you need to free the
result of scm_to_locale_string manually, in order not to get a memory
leak (because apparently it isn't magaged by the bdw gc), so passing
the result directly to strcmp is not a fortunate idea.

Re: Geting the value of a top level scheme value from C

[Mark H Weaver]

Richard Shann <richard@rshann.plus.com> writes:

> Given a C string that is the name of a Scheme variable what is the call
> I need to make from C to get the value?
>
> That is, in the Scheme I have
>
> (define foo "bar")
>
> Then in C I want to write
>
> SCM bar = scm_var_c_get_val ("foo");//imaginary function name

  SCM bar = scm_variable_ref (scm_c_lookup ("foo"));

For better efficiency, do this just once, after 'foo' has been defined:

  SCM foo_var = scm_c_lookup ("foo");

and henceforth just do:

  SCM bar = scm_variable_ref (foo_var);

     Mark

Re: Geting the value of a top level scheme value from C

[Richard Shann]

Thanks for all the replies - sorry I didn't spot that section of the
manual (perhaps because it came under "Using modules" and I haven't
dipped my toes in that stuff).
I have it working now.

Richard

On Fri, 2014-01-24 at 12:34 -0500, Mark H Weaver wrote:
> Richard Shann <richard@rshann.plus.com> writes:
> 
> > Given a C string that is the name of a Scheme variable what is the call
> > I need to make from C to get the value?
> >
> > That is, in the Scheme I have
> >
> > (define foo "bar")
> >
> > Then in C I want to write
> >
> > SCM bar = scm_var_c_get_val ("foo");//imaginary function name
> 
>   SCM bar = scm_variable_ref (scm_c_lookup ("foo"));
> 
> For better efficiency, do this just once, after 'foo' has been defined:
> 
>   SCM foo_var = scm_c_lookup ("foo");
> 
> and henceforth just do:
> 
>   SCM bar = scm_variable_ref (foo_var);
> 
>      Mark