[TOC] ## 定义语句块和语句: ``` program -> stmts -> Stmt Stmts | ε Stmt -> IfStmt | WhileStmt | ForStmt | Function | Block Block -> {Stmts} ``` 整体定义  ## 变量定义 ``` DeclareStmt -> var Variable = Expr ```  ## 变量赋值 ``` AssignStmt -> Variable = Expr ```  ## IfStmt ``` IfStmt -> If(Expr) Block | If(Expr) BLock else Block | If(Expr) Block else IfStmt // 简化:提取公共前缀 IfStmt -> If(Expr) BLock Tail Tail -> else {BLock} | else IfStmt | ε ```  ## Function 定义 ``` Function ->func (Args) Type Block Args -> Type Variable Args | Type Variable | ε ReturnType -> Type | ε Type : int |string |void | bool |string ```