walker_port       544 src/write.c        ScmPort *walker_port = make_walker_port();
walker_port       547 src/write.c        write_walk(obj, walker_port, ctx);
walker_port       548 src/write.c        Scm_ClosePort(walker_port);
walker_port       552 src/write.c        port->data = walker_port->data;