code: func (p *Parser) parseTilde() (Revisioner, error) {
  	var tok token
  	var lit string
  	var err error
  
  	tok, lit, err = p.scan()
  
  	if err != nil {
  		return nil, err
  	}
  
  	switch {
  	case tok == number:
  		n, _ := strconv.Atoi(lit)
  
  		return TildePath{n}, nil
  	default:
  		p.unscan()
  		return TildePath{1}, nil
  	}
  }
docs: // parseTilde extract ~ statements