expression，statement，definition ，identifier(symbol) ,literal(字面量) 术语

expression: an expression evaluates to a value only

statement: a statement containing executable code

definition: a definition instantiating an identifier

identifier(symbol):identifier are tokens(also called symbols) which name language entities

literal(字面量): a value,as opposed to an identifier,written into the source code of a computer program

token:

a lexical token or simply token is a string with an assigned and thus identified meaning,

it its structured as a pair consisting of a token name and an optional token value,

The token name is a category of a lexical unit. Common token names are:

· identifier: names the programmer chooses;

· keyword: names already in the programming language

· separator(also known as punctuators): punctuation characters and paired-delimiters

· operator:symbols that operate on arguments and produce results

· literal:numeric,logical,textual,literals

· comment:line,block

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expression表达式

表达式是 常量、变量、操作符、函数的组合，最后通过计算返回一个值。

这个计算的过程被称作 evaluation

变量也是一个expression因为它代表着内存中的一个值

statement语句

语句包含着可执行代码

(containing executable code)

definition声明

definition会实例化一个identifier

identifier(symbol)

符号表: symbol table.