[gambit-list] C Embedding question

Marc Feeley feeley at iro.umontreal.ca
Thu Jan 29 07:54:44 EST 2009

On 29-Jan-09, at 1:44 AM, Alex Ryu wrote:

> Hello
> I would like to do something similar to the following within my C  
> program:
> *****************
> char* condition = "(2 < 4) & (3 > 7");
> int boole;
> ...
> boole = evaluate(condition);
> *****************
> where evaluate is a scheme function already written and compiled by
> gsc.  Most of the documentation I have seen relates more to the
> reversed situation - calling C functions from scheme.   I have taken a
> look at the client example program in the tests directory, but it is
> not clear to me exactly how the string is treated by scheme - ie, in
> what form it is going to be, if that makes any sense.  Obviously I
> would prefer it as a list of some sort, but I don't know if that's
> possible.  I am using Linux and gcc 4, if that makes a difference.
> Thanks for your time
> Alex

The example code in tests/client.c and tests/server.scm is very close  
to what you want.  One difference is that you want the function to  
return a boolean.  The other difference is that in your example you  
are using an infix expression.  Is this really what you want?  The  
code in tests/server.scm uses Scheme's normal prefix syntax.  If you  
really want infix then you could change the eval-string function in  
tests/server.scm to be

(c-define (evaluate str) (char-string) bool "evaluate" "extern"
     (lambda () (eval (read-from-string (string-append "\\" str  

This will use Gambit's SIX parser (Scheme infix syntax extension).

This is untested code.


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