// Can be called only once per call of next.
Can be called only once per call of next.
// Can be called only once per call of next .
func (l *lexer) backup() {
	if l.width > 0 {
		_ = l.input.UnreadRune()
		l.buffer.Truncate(l.buffer.Len() - l.width)
	}
}
func ( l * lexer ) backup ( ) { if l . width > 0 { _ = l . input . UnreadRune ( ) l . buffer . Truncate ( l . buffer . Len ( ) - l . width ) } }
Can be called only once per call of next.
Can be called only once per call of next .
// An error would be returned if ReadRune wasn't the previous // operation on l.input.