《编译原理第三章形式语言与语法分析.ppt

* * * * CFG for ToyL 变量声明: VarDec ? ? VarDec ? var VarDefList ; 程序: Prg ?VarDec Body 变量定义列表: VarDefList ? VarDef; VarDec ? VarDef ; VarDec Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. CFG for ToyL 变量定义: VarDef ? Type IdList IdList ? id IdList ? id, IdList Type ? int Type ? real Type ? bool Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. CFG for ToyL 程序体: Body ?{ Stms } Stms ? Stm Stm ? Stm; Stms Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. CFG for ToyL 语句: Stm ? Assig | if-S | while-S | read-S | write-S Assig ? id ass Exp If-S ? if Exp then Stms else Stms while-S ? while Exp Body read-S ? read (id) write-S ? write (Exp) Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. CFG for ToyL 表达式: Exp ? E | relE relE ? E E | E E | E=E (1) E ? T (2) E ? E + T (3) E ? E - T (4) T ? F (5) T ? T * F (6) T ? T / F (7) F ? (E) (8) F ? i (9) F ? n Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. * * * * * * * * * * * * * * * * * * * * * * * * * * * CFG小结 CFG (VN,VT, S, P) 可以定义程序设计语言的语法结构; 一般地，VT 是token的集合; 一个VT可以是一个token，一个token-type, 或是代表某种语法结构的一个符号; VN可看作是某种结构的中间表示; 产生式是关于如何推导语法结构的规则; Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 例(1) 算术表达式 VT = {id, num, (, ), +, -, *, /} VN = {Exp} P: Exp ? Exp + Exp Exp ? Exp – Exp Exp ? Exp * Exp Exp ? Exp / Exp Exp ? (Exp) Exp ? id Exp ? num S = Exp Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 例(2) 语句 VT = {id, if, (, ), else, while, {,