一个简单的 TCP 示例 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 242 22.6 解析 IP 地址 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 23 类别）、标点和连接符（Pc 类别）、引号和少许其他字符。 像 + 这样的运算符也是合法的标识符，但是它们会被特别地解析。在一些语境中，运算符可以像变 量一样使用，比如 (+) 表示加函数，语句 (+) = f 会把它重新赋值。大部分 Sm 类别中的 Unicode 中 缀运算符，像 ⊕，则会被解析成真正的中缀运算符，并且支持用户自定义方法（举个例子，你可以 使用语句 const ⊗ = kron 将 ⊗ ⊗ 定义为中缀的 Kronecker 积）。运算符也可以使用修改标记、引号和上 标/下标进行加缀，例如 +̂ₐ″ 被解析成一个与 + 具有相同优先级的中缀运算符。 唯一明确禁止的变量名称是内置关键字的名称： 4.2. 命名规范 19 julia> else = false ERROR: syntax: unexpected "else" julia> try = "No" ERROR: syntax:

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situa�ons. 27.1 Propaga�on of Missing Values The behavior following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract defini�on actually corresponds to a rela�vely natural behavior which is Nothing} arguments or fields. To represent missing data in the sta�s�cal sense (NA in R or NULL in SQL), use the missing object. See the Missing Values sec�on for more details. The empty tuple (()) is

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situa�ons. 27.1 Propaga�on of Missing Values The behavior following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract defini�on actually corresponds to a rela�vely natural behavior which is Nothing} arguments or fields. To represent missing data in the sta�s�cal sense (NA in R or NULL in SQL), use the missing object. See the Missing Values sec�on for more details. The empty tuple (()) is

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situa�ons. 27.1 Propaga�on of Missing Values The behavior following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract defini�on actually corresponds to a rela�vely natural behavior which is Nothing} arguments or fields. To represent missing data in the sta�s�cal sense (NA in R or NULL in SQL), use the missing object. See the Missing Values sec�on for more details. The empty tuple (()) is

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situa�ons. 28.1 Propaga�on of Missing Values The behavior following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract defini�on actually corresponds to a rela�vely natural behavior which is Nothing} arguments or fields. To represent missing data in the sta�s�cal sense (NA in R or NULL in SQL), use the missing object. See the Missing Values sec�on for more details. The empty tuple (()) is

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 27.1 Propagation of Missing Values The behavior following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract definition actually corresponds to a relatively natural behavior which is Nothing} arguments or fields. To represent missing data in the statistical sense (NA in R or NULL in SQL), use the missing object. See the Missing Values section for more details. The empty tuple (()) is

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situa�ons. 29.1 Propaga�on of Missing Values The behavior following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract defini�on actually corresponds to a rela�vely natural behavior which is Nothing} arguments or fields. To represent missing data in the sta�s�cal sense (NA in R or NULL in SQL), use the missing object. See the Missing Values sec�on for more details. The empty tuple (()) is

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 20.1 Propagation of Missing Values missing following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract definition actually corresponds to a relatively natural behavior which is Nothing} arguments or fields. To represent missing data in the statistical sense (NA in R or NULL in SQL), use the missing object. See the Missing Values section for more details. In some languages, the

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 20.1 Propagation of Missing Values missing following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract definition actually corresponds to a relatively natural behavior which is Nothing} arguments or fields. To represent missing data in the statistical sense (NA in R or NULL in SQL), use the missing object. See the Missing Values section for more details. In some languages, the

missing object, which is the singleton instance of the type Missing. missing is equivalent to NULL in SQL and NA in R, and behaves like them in most situations. 20.1 Propagation of Missing Values missing following the well-established rules of three-valued logic which are also implemented by NULL in SQL and NA in R. This abstract definition actually corresponds to a relatively natural behavior which is Nothing} arguments or fields. To represent missing data in the statistical sense (NA in R or NULL in SQL), use the missing object. See the Missing Values section for more details. In some languages, the