clone_var_sym_list
struct var_sym_list *clone_var_sym_list(struct var_sym_list *from_vsl);
data->left_vsl = clone_var_sym_list(left_vsl);
data->right_vsl = clone_var_sym_list(right_vsl);
new_links = clone_var_sym_list(s1->data);
links = clone_var_sym_list(old_state->data);
to_vsl = clone_var_sym_list(one);