Re: simple example to evaluate strings

[Paul Emsley <pemsley@mrc-lmb.cam.ac.uk>]

On 21/12/13 03:57, Josh Stratton wrote:
> I'm completely new to guile and am trying to find a simple example of 
> evaluating a string inside C with some kind of context.  I want to 
> execute small self-contained strings provided by a user.  I've looked 
> at various examples, but everything I've seen seems uses the shell, 
> which seems like more than I need.  The context doesn't need to 
> persist between evals.
>
> Is there an example that would allow me to do something like this?
>
> float evaluateExpression(char* expression)
> {
>     if (!initialized) {
>         scm_init_guile();
>         initialized = true;
>     }
>
>     // making stuff up here
>     some_guile_context = ...
>     some_guile_context.add("someDef", 5); // add some definitionos the 
> expression might expect to be defined
>     some_guile_response = some_guile_context.eval(expression); // 
> expression might use "someDef" like (* someDef 8)
>
>     return scm_arg_to_float(scm_guile_response[0]);
> }

http://www.gnu.org/software/guile/manual/html_node/Fly-Evaluation.html

SCM r = scm_c_eval_string(expression);
if (scm_is_true(scm_number_p(r))
    value = scm_to_double(r);

But you will probably want to wrap the evaluation of expression in a 
scm_catch().

P.