parse.y:5717
void
rb_parser_while_loop(chop, split)
    int chop, split;
{
    if (split) {
	ruby_eval_tree =
	    block_append(NEW_GASGN(rb_intern("$F"),
				   NEW_CALL(NEW_GVAR(rb_intern("$_")),
					    rb_intern("split"), 0)),
				   ruby_eval_tree);
    }
    if (chop) {
	ruby_eval_tree =
	    block_append(NEW_CALL(NEW_GVAR(rb_intern("$_")),
				  rb_intern("chop!"), 0), ruby_eval_tree);
    }
    ruby_eval_tree = NEW_OPT_N(ruby_eval_tree);
}
