By using C you are changing the problem, as your C pointer passes by reference instead of value. The lisp macro works equally well when passing by value, so tr

By using C you are changing the problem, as your C pointer passes by reference instead of value. The lisp macro works equally well when passing by value, so try rewriting your function to operate on a struct (and, not a struct pointer). It is likely that PG was referring to this functionality when asking how to implement this as a function.