code: func (p *Lexer) Integer() (string, bool) {
  
  	var buf []byte
  
  	for {
  		c, _ := p.Byte()
  		if !IsDigit(rune(c)) {
  			break
  		}
  		buf = append(buf, c)
  	}
  
  	p.UnreadByte()
  	return string(buf), len(buf) > 0
  }
docs: // Integer returns true if it finds an (unsigned) integer at the current
  // parser position. It returns also the number found.