code: func NumberToInt(n ast.Number) (*big.Int, error) {
  	r, ok := new(big.Int).SetString(string(n), 10)
  	if !ok {
  		return nil, fmt.Errorf("illegal value")
  	}
  	return r, nil
  }
docs: // NumberToInt converts n to a big int.
  // If n cannot be converted to an big int, an error is returned.