Parsing Expression Grammars and Treetop

1. parsing expression grammars

2. @joaomilho juan maiz joo milho john corn -H E L L O

3. describe DSL do it { should be_valid_ruby } end -D S L

4. Feature Polish notation calculator Scenario Sum Given Ive pressed 4 And then pressed space And then pressed 5 When I press + Then it should display 9 -L A N G U A G E

5. In fact, you do it all the time. Open les, parse stu, turn it into strings, numbers, arrays and link it to code. Like when you wrote your rst CSV parser. (yeah, i know you did it...) You just havent used the right tool. -W R I T E A L A N G U A G E ? W T F ?

6. -C S V grammar CSV rule file (line [n])* line end rule line (value ',')* value end rule value [^,]+ end end

7. - [email protected] PA R S E

8. - [email protected] PA R S E U S E R

9. - [email protected] PA R S E AT

10. [email protected] D O M A I N -PA R S E

11. [email protected] D O T -PA R S E

12. [email protected] C O M P L -PA R S E

13. [email protected] D O T -PA R S E

14. [email protected] C O M P L -PA R S E

15. [email protected] U S E R AT C O M P LD O M A I N D O T D O T C O M P L -PA R S E

16. [email protected] U S E R AT C O M P LD O M A I N D O T D O T C O M P L -PA R S E

17. grammar Email rule full_address user at domain dot compl dot? compl? end rule compl 'co' / 'info' / 'br' / 'il' end end -PA R S E

18. -I N T E R P R E T rule compl 'com' / 'info' / 'br' { def brazil? text_value == 'br' end } end

19. 1 -R E C U R S I O N

20. (1) -R E C U R S I O N

21. ((1)) -R E C U R S I O N

22. (((((((((((((1))))))))))))) -R E C U R S I O N

23. grammar Recursion rule parens '(' parens ')' / '1' end end -R E C U R S I O N

24. -I N T E R P R E T grammar Personnummer rule birthdate [0-9] 6..8 end end

25. -I N T E R P R E T grammar Molecule include Atom include Quantity rule molecule (atom quantity?)+ end end

26. Dened by Noam Chomsky in the 50s. (Yeah, that weird talking guy from the World Social Forum. For your info he is a great linguist.) ! LEX, Yacc Idea: Generates a language -C F G

27. 'if(' exp ')' stmt 'else' stmt | 'if(' exp ')' stmt -C F G O R The dangling else. Consider this:

28. Which alert will be executed? -C F G if(false) if(true) alert('The second if') else alert('The else')

29. Gotcha. None. ! Generally, languages prefer to associate else to the nearest if. ! But this has to be made in a meta rule. -C F G

30. Brian Ford, 2004 http://pdos.csail.mit.edu/~baford/packrat/ Priorities, Not Ambiguities (a / a b) is dierent of (a b / a) Syntactic Predicates (& and !) Regular Expression-Like No left recursion Idea: Recognizes a language -P E G

31. -P E G P R I O R I T Y O P E R AT O R The dangling else xed. 'if(' exp ')' stmt 'else' stmt / 'if(' exp ')' stmt

32. Result linear time parsing using memoization one and only one valid parse tree no dangling else cases easier to learn and use Drawbacks still new memory eater not suitable for NLP -P E G

33. treetop.rubyforge.org rubyconf2007.confreaks.com/d1t1p5_treetop.html Nathan Sobo (Pivotal Labs), Cliord Heath, Nick Kallen & more. -T R E E T O P

34. arithmetic + lambda calculus + sql 0xCOFFEE full lang compiled to LLVM html css json odp hapag dcf scheme apache conf trxl lolcode card sloc hairball (haml) lordbishop (names) -T R E E T O P

35. Citrus, Parsley, NEG Ruby tynirb: peg/leg C Rats! Java PetitParser SmallTalk ppeg, pyPEG, pyparsing Python Frisby, Leafy Haskell Perl6 rules Perl6 native! -O U T T H E R E

36. brain fuck

37. 3000 slots -B R A I N F U C K 0 0 0 0 0 0 0 0 0

38. -B R A I N F U C K 0 0 0 0 0 0 0 0 0 >

39. -B R A I N F U C K 0 0 0 0 0 0 0 0 0

40. -B R A I N F U C K 0 0 0 0 0 0 0 0 0 <

41. -B R A I N F U C K 1 0 0 0 0 0 0 0 0 +

42. -B R A I N F U C K 0 0 0 0 0 0 0 0 0 -

43. -B R A I N F U C K 0 0 0 0 0 0 0 0 0 ,

44. -B R A I N F U C K 66 0 0 0 0 0 0 0 0 , B

45. -B R A I N F U C K 66 0 0 0 0 0 0 0 0 . B

46. -B R A I N F U C K 66 0 0 0 0 0 0 0 0 []

47. -B R A I N F U C K [>+] 66 0 0 0 0 0 0 0 0

48. -B R A I N F U C K 66 1 1 1 1 1 1 1 1 [>+]

49. +++[>+++[>+++++++< +++[>++++++. +++++ +++++++. -------- . ++. +. ---. < +++[>++. -. +++. ----.

Parsing Expression Grammars and Treetop

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