1. 贺天行

2.  First please download to appetitzer in our webpage  This tutorial will be mainly about codes provided in the appetizer

4.  Jflex  JCup(and the runtime mentioned above) .flex and.cup(contained in appetizer)  Symbols.java(generated by cup)  Yylex.java(generaged by flex)  Parser.java(generated by cup)

5. i = i + 2 ; ID(i) EQUAL ID(i) PLUS NUMBER(2) SEMI

6.  See Jflex manual to see the definition RE. Example: Digits=[0-9]*

7.  Can any RE be converted to an NFA? & can any NFA be converted to a DFA?

8.  Use.bat to help you  Now we just run jflex.bat 1.flex to generate

10.  Symbols.java is just a mapping(token2int) table.  It enables Yylex to pass tokens: %implements Symbols "(" { return tok(LPAREN); }

11.  The scanner will generate series of java_cup.runtime.Symbol so we can use this to test our Scanner.

12.  ScannerTest(download).

13.  We require to exit(1) when an error is found.  Your program are not supposed to throw exception upon an compile error.

14.  What does \\t here mean?\\t

16.  How to use RE to express ((()))?

19. F=(F)|epilson

20.  If a1…an can be reduced to s  Q:what’s a CFG for something like ()()(((())))?  Q:among T,N,s, which is the output of Flex? Given a context-free gramar G, What’s the language L(G)?

21.  We say a grammar is ambiguous when it has more than one parse tree for some string.  a bad grammar  One way to deal with ambiguous grammar is to write a unambiguous grammar.  A good one

22. Instead of rewriting the grammar – Use the more natural (ambiguous) grammar – Along with disambiguating declarations Most tools allow precedence and associativity -(like cup)declarations to disambiguate grammars

23.  For you to understand better about what cup is doing, I need to introduce a bit how a parser is constructed.  You need to read Ch4 in dragon book for complete knowledge.

25.  Shift : move in another token  Reduce : use a production rule

30.  Algorithm 4.46

32.  Given a grammar G, what is FOLLOW(A) for nonterminal A? The set of terminals a that can appear immediately to the right of A in some sentential form

34.  Don’t mess these two up. The Symbol class here is to provide a unique object to hold each string literal  This unique Symbol will be useful in later phase

37.  Every class derives from Stmt, so we add this line  Then we get className in the output

38. selection-statement: 'if' '(' expression ')' statement ('else' statement)? precedence right ELSE; if then if then : else else at this point, we can both shift/reduce, however, we assigned ELSE a higher precedence, so it will be shifted.

39.  The output in ScannerTest and ParserTest will show you what results you get from Flex and Cup. They can greatly help your debugging.

40. Like :  How is Symbols.java used in flex?  How do you handle string in flex? So, please carefully read the manual