librep

John Harper writes:
 > Jesse Marlin writes:
 > |I want to pass a lisp list to a C function using librep.  The list will be
 > |the equivalent of ORing a number of options together, and I was just
 > |wondering how this will be represented in C land.  An indexed array,
 > |a linked list?  Thanks.
 > 
 > I'm not sure I fully understand the question. But if you pass any lisp
 > object to a C function it's passed as a `repv' value -- this is just a
 > piece of (typed) lisp data.
 > 
 > As you know, lists are built from cons cells, you can use the macros
 > rep_CONSP, rep_CAR and rep_CDR to access the values of the list from C,
 > as you would do in lisp. E.g.
 > 
 > void
 > my_function (repv list)
 > {
 >     repv first, second;
 > 
 >     if (rep_CONSP (list))
 >     {
 > 	/* `list' is a cons, so can safely refer to the first object */
 > 	first = rep_CAR (list);
 > 
 > 	if (rep_CONSP (rep_CDR (list)))
 > 	{
 > 	    /* the cdr of `list' is also a cons */
 > 	    second = rep_CAR (rep_CDR (list));
 > 	}
 > 	else
 > 	    error handling;
 >     }
 >     else
 > 	error handling;
 > 
 >     do something with `first' and `second'...
 > }

 Thanks, that's what I was looking for, not the code, but how to traverse
the list in C.

 > 
 > if you find that you're doing too much list manipulation in C code, it
 > usually means that your design may need rethinking, so that more of the
 > code can be written in lisp!

 I was just looking for way to pass options via a list so that I could
 OR them together in C land.

  my_function (OPTION1 | OPTION2 | OPTION3)

 > 
 > 	John
 > 
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