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编译程序 的面向对象设计与 实现

编译程序 的面向对象设计与 实现. Dr. Zheng Xiaojuan Associate Professor Software College of Northeast Normal University April. 2009. 阶段三: 语法分析器开发. 项目需求. 读入词法分析的输出结果 token 序列; 对 token 序列进行语法分析生成语法正确的与源程序结构相对应的语法分析树; 能够指出语法错误所在位置。. 一、编译原理内容. 语法分析程序的功能. 所需编译知识关联图. √. Top-down. using. √.

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编译程序 的面向对象设计与 实现

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  1. 编译程序的面向对象设计与实现 Dr. Zheng Xiaojuan Associate Professor Software College of Northeast Normal University April. 2009

  2. 阶段三:语法分析器开发

  3. 项目需求 • 读入词法分析的输出结果token序列; • 对token序列进行语法分析生成语法正确的与源程序结构相对应的语法分析树; • 能够指出语法错误所在位置。

  4. 一、编译原理内容

  5. 语法分析程序的功能

  6. 所需编译知识关联图 √ Top-down using √ Syntax definition Context Free Grammar implement basing on Bottom-up Develop a Parser

  7. 所需编译知识关联图 using Syntax definition CFG check precondition first() basing on Predict(A) Yes Top-down parsing follow(A) Recursive-descent Implement LL(1)

  8. 一、Context Free Grammar (CFG) • 定义为四元组(VT,VN,S,P) • VT是有限的终极符集合 • VN是有限的非终极符集合 • S是开始符,S VN • P是产生式的集合,且具有下面的形式: AX1X2…Xn 其中AVN,Xi(VTVN) ,右部可空。

  9. 二、Top-down parsing • 自顶向下语法分析方法的前提条件 • G = (VT, VN, S, P) • For any A VN, • For any two productions of A, • Predict(A  1) Predict(A  2) =  (同一个非终极符的任意两个产生式的predict集合互不相交) • 这个条件保证:针对当前的符号和当前的非终极符,可以选择唯一的产生式来进行推导;

  10. 三、 Grammar Transformation • 消除公共前缀(left factoring) • 公共前缀 • A  1 | … | n| 1|…| m • 提取公因子 • A  A’| 1|…| m • A’ 1 | … | n

  11. 消除左递归(left recursion) • 直接左递归:A  A(1 | … |  n)|1|…| m • 消除方法: A  (1|…| m)A’ A’ (1| … | n)A’|

  12. 消除左递归(left recursion) • 间接左递归: • 消除方法: • Pre-conditions • Algorithm S  A b A  S a | b 1:S 2:A A  Aba | b A  bA’ A’  baA’ | 

  13. 四、Three Important Sets • First Set(first集) for a string  with non-terminal and terminal symbols; • First() • Follow Set(follow集) for a non-terminal symbol A; • Follow(A) • Predict Set(预测集) for a production; • Predict(A )

  14. 1 First Set (first集) • Definition: • First() = {a | *a, aVT}, • if * then First()= First()  {} • How to calculate First()? •  = , First() = {} •  = a, aVT, First() = {a} •  = A, AVN, First() =First(A) •  = X1 X2 …… Xi-1 Xi …… Xn

  15. For each symbol X, calculate First(X) • S = {A | A * , AVN} • For each terminal symbol a, First(a) = {a} • VN={A1, …, An} , calculate First(Ai) • 初始化, First(Ai) ={}; • for i =1 to n 对于Ai的每个产生式, - if Ai, First(Ai) = First(Ai)  {}; - if AiY1 …. Ym, {Y1 ,…. ,Ym}S, First(Ai) = First(Ai)  First(Y1)  …..  First(Ym) - if AiY1 …. Ym, {Y1 ,…. ,Yj-1}S, Yj  S First(Ai) = {First(Ai)  {First(Y1)  …..  First(Yj-1)-{}}  First(Yj) (3) Repeat (2) until 每个First(Ai)没有变化(收敛).

  16. Example S = {E’, T’} P: (1) E  TE’ (2) E’ + TE’ (3) E’  (4) T  FT’ (5) T’ * F T’ (6) T’  (7) F  (E) (8) F  i (9) F  n

  17. 2 Follow Set (follow集) • How to calculate Follow(A), AVN (1)初始化, AVN, Follow(A) = { } (2)Follow(S) = {#} (3)对于每个产生式A  • If there is no non-terminal symbol in , skip; • If  = B, BVN, Follow(B) = Follow(B)  (First()-{}) • If First(), Follow(B) = Follow(B)  Follow(A) • If  = B, Follow(B) = Follow(B)  Follow(A) (4) Repeat (3) until all follow sets do not change any more;

  18. Example P: (1) E  TE’ (2) E’ + TE’ (3) E’  (4) T  FT’ (5) T’ * F T’ (6) T’  (7) F  (E) (8) F  i (9) F  n

  19. 3 Predict Set (predict集) • Definition: • Predict(A  ) = first(), if   first(); • Predict(A  ) = (first()- )  follow(A), if   first();

  20. first集 Example P: (1) E  TE’ (2) E’ + TE’ (3) E’  (4) T  FT’ (5) T’* F T’ (6) T’  (7) F  (E) (8) F  i (9) F  n First(TE’)={i, n,( } First(+TE’)={+} Follow(E’)={#, )} follow集 First(FT’)={i,n,( } First(*FT’)={*} Follow(T’)={ ),+, # } First((E))={ ( } First(i)={i} First(n)={n}

  21. 五、 Recursive-Descent Parsing • The goal of parsing • Check whether the input string belongs to the language of CFG; • Two actions • match(a): to check current symbol, if match, read next symbol; • Derivation: select the production

  22. General Process • For each A  VN, • A  1|……| n A( ) { case token of Predict(A  1): SubR(1) ; break; …… Predict(A  n): SubR(n) ; break; other: error; } • G = (VT, VN, S, P) • Predefined function: void match(a: VT) • Global variable: token: VT • Input string: str

  23. General Process SubR(): • = X1 X2 …… Xn If Xi VT, match(Xi) If Xi VN, Xi(); void match(a: VT) { if token == a token = readNext(str); else error(); } SubR(): • =  { }

  24. Example Z ( ) { if token = a {match(a); B( ); match(d); } else error( ); } B ( ) { case token of d: match(d);break; c: match(c); break; b:{ match(b); B( ); break;} other: error( ); } P: (1) Z  aBd {a} (2) B  d {d} (3) B  c {c} (4) B  bB {b} a b c d main( ){ read(token); Z( )}

  25. Building Parse Tree • Data structure • ParseTree • Operations • ParseTree BuildRoot(symbol: VT  VN); • ParseTree BuildOneNode(symbol: VT VN) • AddOneSon(father:*ParseTree, son:*ParseTree ) • SetNum(Node:*ParseTree, n:int) 符号 儿子个数 儿子指针

  26. Example Z ( ) { if token = a { match(a); B( ); match(d); } else {error(); return nil;} } *ParseTree SetNum(T, 3); T = BuildRoot(Z); A = BuildOneSon(a); AddOneSon(T, A); AddOneSon(T, BB); BB= D = BuildOneSon(d); AddOneSon(T, D); return T;

  27. 六、 LL(1) Parsing Method • LL(1) Parsing • LL(1) parsing table to record predict sets for each production; (LL(1)分析表) • A general engine(一个通用的驱动程序)

  28. LL(1) Parsing Table (LL(1)分析表) • How to build LL(1) Parsing Table for a LL(1) Grammar? • For a LL(1) Grammar G = (VT, VN, S, P) • VT = {a1, …, an} • VN = {A1, …, An} • LL(Ai, ai) = [Ai  ], if aipredict(Ai ) • LL(Ai, ai) = error, if ai not belong to the predict set of any production of Ai

  29. LL(1) Parsing Mechanism a … … … # X Input … 驱动程序:  栈为空情形的处理 X VT情形的处理 X VN情形的处理 … Stack LL[1]分析表

  30. LL(1) Parsing Engine [1] 初始化: Stack := [ ];Push(S); [2] 读下一个输入符: Read(a); [3] 若当前格局是( , # ),则成功结束;否则转下; [4] 设当前格局为(..... X, a.....),则  若X VT & X= a ,则 { Pop(1); Read(a);goto [3] } 若X VT & X a ,则Error; 若X  VN ,则: if LL(X, a)=X→Y1 Y2 ...... Yn then { Pop(1);Push(Yn ,.....,Y1);goto[3] } else Error

  31. Building Parse Tree During LL(1) [1] 初始化: Stack := [ ]; root=BuildOneNode(S); Push(S, root); [2] 读下一个输入符: Read(a); [3] 若当前格局是( , # ),则成功结束;否则转下; [4] 设当前格局为(..... X, a.....),则 若X VT & X= a ,则 { Pop(1); Read(a);goto [3] } 若X VT & X a ,则Error; 若X  VN ,则: if LL(X, a)=X→Y1 Y2 ...... Yn then { (X, ptr) =Pop(1); for i=n to 1 { p[i] = BuildOneNode(Yi), Push(Yi, p[i]);} AddSons(ptr, p, n); goto[3] } else Error

  32. 二、语法分析程序的实现

  33. 部分SNL语言的上下文无关文法 总程序: Program ::= ProgramHead DeclarePart ProgramBody . 程序头: 2) ProgramHead ::= PROGRAM ProgramName 3) ProgramName ::= ID 程序声明: DeclarePart ::= TypeDecpart VarDecpart ProcDecpart 类型声明: TypeDecpart ::=  | TypeDec TypeDec ::= TYPE TypeDecList TypeDecList ::= TypeId = TypeDef ; TypeDecMore TypeDecMore ::=  | TypeDecList TypeId ::= ID

  34. 语法树节点的数据结构 原则:语法分析器的输出将作为语义分析的输入,因此语法分析树中不仅应该包含源程序的结构信息,还应该为语义分析提供必要的信息。在进行语法分析时,语法分析程序将根据源语言的文法产生式,为相应的非终极符创建一个语法树节点,并为之赋值,得到的是与程序结构相似的改进的语法树。除此之外,只要能够清晰表达出源程序的语法结构即可。语法树节点的数据结构 可小组自行定义。

  35. 语法树节点的数据结构

  36. program p type t1 = integer; var integer v1,v2; procedure q(integer i); var integer a; begin a:=i; write(a) end begin read(v1); if v1<10 then v1:=v1+10 else v1:=v1-10 fi; q(v1) end. ProK PheadK p TypeK DecK IntegerK t1 VarK DecK IntegerK v1 v2 ProcDecK q DecK value param: IntegerK i VarK DecK IntegerK a StmLk StmtK Assign ExpK a IdV ExpK i IdV StmtK Write ExpK a IdV StmLk StmtK Read v1 StmtK If ExpK Op < ExpK v1 IdV ExpK Const 10 StmtK Assign ExpK v1 IdV ExpK Op + ExpK v1 IdV ExpK Const 10 StmtK Assign ExpK v1 IdV ExpK Op - ExpK v1 IdV ExpK Const 10 StmtK Call ExpK q IdV ExpK v1 IdV

  37. 第三次小组讨论题目: 明确项目需求,学习ppt编译原理六个知识点后完成: • 仔细研究源语言的语法规则定义,确定产生式是否存在冲突,如有冲突请根据知识点三进行文法的转换。 • 根据知识点四求出没有冲突的文法的每条产生式的三个集合。 • 根据源语言的语法规则特点定义语法分析树的数据结构。 • 根据知识点五或六进行语法分析(小组任选方法之一)。语法错误可输出一次。 • 讨论语法分析树的建立与输出(如对树的数据结构描述不清楚请进行小组复习或个人复习) • 应用UML建立系统类图、对象图、用例图、交互图、活动图、状态图等,编制相应的说明文档。

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