p.print(msg + " (")
	const tab = ". "
	p.indent = append(p.indent, tab...)
	return func() {
		p.indent = p.indent[:len(p.indent)-len(tab)]
		if x := recover(); x != nil {
			panic(x) // skip print_trace
		}
		p.print(")")
	}
}

func (p *parser) print(msg string) {
	fmt.Printf("%5d: %s%s\n", p.line, p.indent, msg)
}