Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -2- 阶段三：语法分析器开发

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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。

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -4- 一、编译原理内容

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -5- 语法分析程序的功能

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -6- 所需编译知识关联图 Develop a Parser Syntax definition basing on Context Free Grammar using implement Top-down Bottom-up √ √

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -7- Top-down parsing Syntax definition basing on CFG using check precondition Predict(A  ) first(  ) follow(A) Yes Recursive-descent LL(1) Implement 所需编译知识关联图

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -8- 一、 Context Free Grammar (CFG) 定义为四元组 (V T,V N,S,P)  V T 是有限的终极符集合  V N 是有限的非终极符集合  S 是开始符， S  V N  P 是产生式的集合，且具有下面的形式： A  X 1 X 2 … X n 其中 A  V N ， X i  (V T  V N ) ，右部可空。

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -9- 二、 Top-down parsing 自顶向下语法分析方法的前提条件 –G = (V T, V N, S, P) –For any A  V N, –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 ;

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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 ’ | 

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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 ’ | 

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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   )

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques First Set (first 集 ) Definition: –First(  ) = {a |  *a , a  V T }, –if  *  then First(  )= First(  )  {  } How to calculate First(  )? –  = , First(  ) = {  } –  = a, a  V T, First(  ) = {a} –  = A, A  V N, First(  ) = First(A) –  = X 1 X 2 …… X i-1 X i …… X n

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -15- S  = {A | A  * , A  V N } For each terminal symbol a, First(a) = {a} For each symbol X, calculate First(X) V N ={A 1, …, A n }, calculate First(A i ) (1) 初始化, First(A i ) ={}; (2)for i =1 to n 对于 A i 的每个产生式, - if A i  , First(A i ) = First(A i )  {  }; - if A i  Y 1 …. Y m, {Y 1,….,Y m }  S , First(A i ) = First(A i )  First(Y 1 )  …..  First(Y m ) - if A i  Y 1 …. Y m, {Y 1,….,Y j-1 }  S , Y j  S  First(A i ) = {First(A i )  {First(Y 1 )  …..  First(Y j-1 )-{  }}  First(Y j ) (3) Repeat (2) until 每个 First(A i ) 没有变化 ( 收敛 ).

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -16- 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 S  = {E ’, T ’ } E{i, n, ( } E’ { +,  } T{ i, n, ( } T’ { *,  } F{ i, n, ( }

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques Follow Set (follow 集 ) How to calculate Follow(A), A  V N (1) 初始化,  A  V N, 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  V N, 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;

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -18- Example E{i, n, ( } E’ { +,  } T{ i, n, ( } T’ { *,  } F{ i, n, ( } 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 E{#, )} E’{#, )} T{+, ), #} T’{+, ), #} F{*, +, ), #}

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques Predict Set (predict 集 ) Definition: –Predict(A   ) = first(  ), if   first(  ); –Predict(A   ) = (first(  )-  )  follow(A), if   first(  );

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -20- Example E{i, n, ( } E’ { +,  } T{ i, n, ( } T’ { *,  } F{ i, n, ( } 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 E{#, )} E’{#, )} T{+, ), #} T’{+, ), #} F{*, +, ), #} first 集 follow 集 First(TE ’ )={i, n,( } First(+TE ’ )={+} Follow(E ’ )={#, )} First(FT ’ )={i,n,( } First(*FT ’ )={*} Follow(T ’ )={ ),+, # } First((E))={ ( } First(i)={i} First(n)={n}

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -22- General Process G = (V T, V N, S, P) Predefined function: void match(a: V T ) Global variable: token: V T Input string: str For each A  V N, A   1 |……|  n A( ) { case token of Predict(A   1 ): SubR(  1 ) ; break; …… Predict(A   n ): SubR(  n ) ; break; other: error; }

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -23- General Process void match(a: V T ) { if token == a token = readNext(str); else error(); } SubR(  ):  = X 1 X 2 …… X n If X i  V T, match(X i ) If X i  V N, X i (); SubR(  ):  =  { }

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -24- Example P: (1) Z  aBd {a} (2) B  d {d} (3) B  c {c} (4) B  bB {b} 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( ); } a b c d main( ){ read(token); Z( )}

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -25- Building Parse Tree Data structure –ParseTree Operations –ParseTree BuildRoot(symbol: V T  V N ); –ParseTree BuildOneNode(symbol: V T  V N ) –AddOneSon(father:*ParseTree, son:*ParseTree ) –SetNum(Node:*ParseTree, n:int) 符号 儿子个数 儿子指针

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -26- Example Z ( ) { if token = a { match(a); B( ); match(d); } else {error(); return nil;} } *ParseTree T = BuildRoot(Z); AddOneSon(T, A);A = BuildOneSon(a); AddOneSon(T, BB); BB= AddOneSon(T, D);D = BuildOneSon(d); return T; SetNum(T, 3);

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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 )

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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 = (V T, V N, S, P) –V T = {a 1, …, a n } –V N = {A 1, …, A n } –LL(A i, a i ) = [A i   ], if a i  predict(A i   ) –LL(A i, a i ) = error, if a i not belong to the predict set of any production of A i a1a1 …anan # A1A1 ……. … AnAn

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -29- LL(1) Parsing Mechanism Stack Input #………a 驱动程序 :  栈为空情形的处理  X  V T 情形的处理  X  V N 情形的处理 X … … LL[1] 分析表

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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  V T & X= a ，则 { Pop(1) ； Read(a) ； goto [3] }  若 X  V T & X  a ，则 Error ；  若 X  V N ，则： if LL(X, a)=X→Y 1 Y Y n then { Pop(1) ； Push(Y n,.....,Y 1 ) ； goto[3] } else Error

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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  V T & X= a ，则 { Pop(1) ； Read(a) ； goto [3] }  若 X  V T & X  a ，则 Error ；  若 X  V N ，则： if LL(X, a)=X→Y 1 Y Y n then { (X, ptr) = Pop(1); for i=n to 1 { p[i] = BuildOneNode(Yi), Push(Y i, p[i]) ； } AddSons(ptr, p, n); goto[3] } else Error

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -32- 二、语法分析程序的实现

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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::=PROGRAMProgramName 3) ProgramName::= ID 程序声明： DeclarePart::=TypeDecpart VarDecpart ProcDecpart 类型声明： TypeDecpart::=  | TypeDec TypeDec ::= TYPETypeDecList TypeDecList::=TypeId = TypeDef ; TypeDecMore TypeDecMore::=  | TypeDecList TypeId::= ID

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -34- 语法树节点的数据结构 childSiblingLinenonodekindkindidnumnametableattrtype 012de c stmtexp…… 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。

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -35- 语法树节点的数据结构

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -36- 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 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.

Software College of Northeast Normal University Compiler Construction Principles & Implementation Techniques -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。