#                else if(car == _symbol("mapcar"))
#                    return _mapcar(_eval3(_cadr(form), env, env, d+1),
#                                   _eval3(_caddr(form), env, env, d+1),
#                                   env, d+1)

}
# this is dead code. i tried to make it iterative and write it in awk
# so it would be faster, but it ended up eval-ing things too many
# times and i couldn't figure out where the problem was, even with
# copious debug logging.
function _mapcar(fun, lis, env, d,  v, app, acc) {
    if(_is_null(lis)) {
        return lis
    } else {
        # fun and lis are already evaluated
        logg_dbg("_mapcar", "fun: " _repr(fun) "; lis: " _repr(lis), d)
        for(acc=_nil(); !_is_null(lis); lis = _cdr(lis)) {
            app = _cons(fun, _cons(_car(lis),
                                   _nil()))
            logg_dbg("_mapcar", "evaling: " _repr(app), d)
            v = _eval(app, d+1)
            logg_dbg("_mapcar", "result: " _repr(v))
            acc = _cons(v, acc)
        }
        return _nreverse(acc)
    }