06-03-recursive-descent-parsing-annotated

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1、CompilersRecursiveDescentParsingAlexAikenRecursiveDescent•Theparsetreeisconstructed–Fromthetop1–Fromlefttorightt3t2947•Terminalsareseeninorderofappearanceinthetokenstream:ttt568t2t5t6t8t9AlexAikenRecursiveDescent•ConsiderthegrammarET

2、T+ETint

3、int*T

4、(E)•Tokenstreamis:(int5)•Start

5、withtop-levelnon-terminalE–TrytherulesforEinorderAlexAikenRecursiveDescentET

6、T+ETint

7、int*T

8、(E)E(int)5AlexAikenRecursiveDescentET

9、T+ETint

10、int*T

11、(E)ET(int)5AlexAikenRecursiveDescentET

12、T+ETint

13、int*T

14、(E)ETMismatch:intdoesnotmatch(intBacktrack…(int)5AlexAikenRecursiveDescentET

15、

16、T+ETint

17、int*T

18、(E)ET(int)5AlexAikenRecursiveDescentET

19、T+ETint

20、int*T

21、(E)ETMismatch:intdoesnotmatch(int*TBacktrack…(int)5AlexAikenRecursiveDescentET

22、T+ETint

23、int*T

24、(E)ET(int)5AlexAikenRecursiveDescentET

25、T+ETint

26、int*T

27、(E)ETMatch!Advanceinput.(E)(int)5AlexAikenRecursiveDescentE

28、T

29、T+ETint

30、int*T

31、(E)ET(E)(int)5AlexAikenRecursiveDescentET

32、T+ETint

33、int*T

34、(E)ET(E)T(int)5AlexAikenRecursiveDescentET

35、T+ETint

36、int*T

37、(E)ETMatch!Advanceinput.(E)T(int)5intAlexAikenRecursiveDescentET

38、T+ETint

39、int*T

40、(E)ETMatch!Advanceinput.(E)T(int)5intAlexAikenRecursiveDescentET

41、

42、T+ETint

43、int*T

44、(E)ETEndofinput,accept.(E)T(int)5intAlexAikenChoosethederivationthatisavalidrecursivedescentERecursiveDescentparseforthestringid+idinthegivengrammar.MovesE’thatarefollowedbybacktrackingaregiveninred.-E’EE’

45、E’+EidE(E)E’-E’

46、id

47、(E)E’E’+EE’+E-E’+Eid+Eid+Eid+E’Eid+E’

48、id+idE’id+-E’idid+idE’+EEid+EE’+Eid+E’id+Eid+idid+E’id+id