guile's eval from C

guile's eval from C

[Viktor Pavlenko]

Hello and sorry for the simple question.

I'd like to evaluate an SCM object from C, equivalent to

guile> (eval '(car '("a" "b" "c")))
"a"
guile> (eval "a")
"a"

Looks like the best way is to call gh_call1(), but how do I get an SCM
object for guile's eval? I could also build a C string containing the
complete expression to be evaluated ( "(eval '(car '("a" "b" "c")))" )
and call gh_eval_str() but this seems inefficient because I have the
expression to be evaluated as SCM object.

Thank you in advance.

Viktor


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Re: guile's eval from C

[Rob Browning]

Viktor Pavlenko <vvp@rogers.com> writes:

> I'd like to evaluate an SCM object from C, equivalent to
>
> guile> (eval '(car '("a" "b" "c")))
> "a"
> guile> (eval "a")
> "a"

  SCM mylist = gh_eval_str ("(car '(\"a\" \"b\" \"c\"))");

or depending on your needs, perhaps:

  SCM somelist = SCM_EOL;
  ...
  mylist = scm_cons (scm_makfrom0str ("c"), somelist);
  ...
  mylist = scm_cons (scm_makfrom0str ("b"), somelist);
  ...
  mylist = scm_cons (scm_makfrom0str ("a"), somelist);
  ...
  SCM result = SCM_CAR (somelist);

This presumes you're using 1.6.0.  If you're not, then you may have to
substitute some gh_* functions for the above...

> Looks like the best way is to call gh_call1(), but how do I get an SCM
> object for guile's eval? I could also build a C string containing the
> complete expression to be evaluated ( "(eval '(car '("a" "b" "c")))" )
> and call gh_eval_str() but this seems inefficient because I have the
> expression to be evaluated as SCM object.

Alternately, I believe you could use this:

  scm_eval (some_expression, scm_c_resolve_module ("some module"));

though I haven't tested it and so the resolve_module call may need a
little adjustment...

Hope this helps.

-- 
Rob Browning
rlb @defaultvalue.org, @linuxdevel.com, and @debian.org
Previously @cs.utexas.edu
GPG=1C58 8B2C FB5E 3F64 EA5C  64AE 78FE E5FE F0CB A0AD


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Re: guile's eval from C

[Neil Jerram]

>>>>> "Viktor" == Viktor Pavlenko <vvp@rogers.com> writes:

    Viktor> Hello and sorry for the simple question.
    Viktor> I'd like to evaluate an SCM object from C, equivalent to

    guile> (eval '(car '("a" "b" "c")))
    Viktor> "a"
    guile> (eval "a")
    Viktor> "a"

    Viktor> Looks like the best way is to call gh_call1(), but how do
    Viktor> I get an SCM object for guile's eval? I could also build a
    Viktor> C string containing the complete expression to be
    Viktor> evaluated ( "(eval '(car '("a" "b" "c")))" ) and call
    Viktor> gh_eval_str() but this seems inefficient because I have
    Viktor> the expression to be evaluated as SCM object.

One possibility is:

  scm_primitive_eval (exp);

This will evaluate the supplied expression in the current module.

Does this help?

        Neil



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Re: guile's eval from C

[Viktor Pavlenko]

>>>>> "NJ" == Neil Jerram <neil@ossau.uklinux.net> writes:

>>>>> "Viktor" == Viktor Pavlenko <vvp@rogers.com> writes:
    Viktor> Hello and sorry for the simple question.
    Viktor> I'd like to evaluate an SCM object from C, equivalent to

    guile> (eval '(car '("a" "b" "c")))
    Viktor> "a"
    guile> (eval "a")
    Viktor> "a"

    Viktor> Looks like the best way is to call gh_call1(), but how do
    Viktor> I get an SCM object for guile's eval? I could also build a
    Viktor> C string containing the complete expression to be
    Viktor> evaluated ( "(eval '(car '("a" "b" "c")))" ) and call
    Viktor> gh_eval_str() but this seems inefficient because I have
    Viktor> the expression to be evaluated as SCM object.

    NJ> One possibility is:

    NJ>   scm_primitive_eval (exp);

    NJ> This will evaluate the supplied expression in the current module.

    NJ> Does this help?

I believe it will when I switch to 1.6. Thanks!

Viktor


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