The document discusses dynamic grammars, which allow grammars to be modified at runtime. This enables features like late-bound behavior, first-class representation of grammars, on-the-fly transformation of grammars, and introspection and reflection. Dynamic grammars provide benefits like enabling language and tool extensions through language boxes that isolate languages, and allowing host languages to change other languages' grammars through grammar transformations.

1. Dynamic Grammars
Lukas Renggli, Stéphane Ducasse,
Tudor Gîrba, Oscar Nierstrasz

2. grammar
a set of rules governing what
strings are valid or allowable
in a [formal] language.
[Adapted from The New Oxford American Dictionary on Grammar]

3. dynamic grammar
a high-level grammar that
executes at runtime behaviors
that other grammars perform
during compilation, see
dynamic languages.
[Adapted from Wikipedia on Dynamic Programming Languages]

4. Dynamic Grammars
Dynamic Languages
‣ Late-bound behavior
‣ First-class representation
‣ On-the-fly transformation
‣ Introspection and reflection

5. Why would
we want that?

6. Language and Tool Extensions
Language Boxes
Host Environment

7. Language and Tool Extensions
Language Boxes
Grammars
Dynamic
Host Environment

8. Language
*
Change
Language * Language
Box Concern
*
* Language
Scope

9. Language
Change
=
δ Host Language
Grammar

10. Language Grammar
=
Change Transformation

11. scanIdentifier
self step.
((currentCharacter between: $A and: $Z) or:
[ currentCharacter between: $a and: $z ]) ifTrue: [
[ self recordMatch: #IDENTIFIER.
self step.
(currentCharacter between: $0 and: $9)
or: [ (currentCharacter between: $A and: $Z) or:
[ currentCharacter between: $a and: $z ] ] ]
whileTrue.
^ self reportLastMatch ]

12. ✖
scanIdentifier
self step.
((currentCharacter between: $A and: $Z) or:
[ currentCharacter between: $a and: $z ]) ifTrue: [
[ self recordMatch: #IDENTIFIER.
self step.
(currentCharacter between: $0 and: $9)
or: [ (currentCharacter between: $A and: $Z) or:
[ currentCharacter between: $a and: $z ] ] ]
whileTrue.
^ self reportLastMatch ]

13. #( #[1 0 9 0 25 0 13 0 34 0 17 0 40 0 21 0 41]
#[1 0 9 0 25 0 13 0 34 0 93 0 76 0 157 0 112]
#[1 2 38 0 21 2 38 0 25 2 38 0 26 0 13 0 34]
#[0 1 154 0 16 0 21 0 25 0 26 0 34 0 40 0 41]
#[0 1 210 0 76 0 81]
#[0 1 214 0 76 0 81]
#[1 0 173 0 76 0 177 0 81]
#[0 1 134 0 16 0 21 0 25 0 26 0 34 0 40 0 41]
#[1 1 46 0 21 1 46 0 25 1 46 0 26 1 69]
#[1 1 54 0 21 1 54 0 25 1 54 0 26 1 54 0 34]
#[0 2 102 0 21 0 25 0 26 0 34 0 40 0 41 0 76]
#[0 2 50 0 21 0 25 0 26 0 76 0 79]
#[1 1 13 0 76 2 85 0 124 1 21 0 125]
#[1 2 89 0 17 2 30 0 21 2 30 0 82]
#[1 2 93 0 21 2 97 0 82] )

14. ✖
#( #[1 0 9 0 25 0 13 0 34 0 17 0 40 0 21 0 41]
#[1 0 9 0 25 0 13 0 34 0 93 0 76 0 157 0 112]
#[1 2 38 0 21 2 38 0 25 2 38 0 26 0 13 0 34]
#[0 1 154 0 16 0 21 0 25 0 26 0 34 0 40 0 41]
#[0 1 210 0 76 0 81]
#[0 1 214 0 76 0 81]
#[1 0 173 0 76 0 177 0 81]
#[0 1 134 0 16 0 21 0 25 0 26 0 34 0 40 0 41]
#[1 1 46 0 21 1 46 0 25 1 46 0 26 1 69]
#[1 1 54 0 21 1 54 0 25 1 54 0 26 1 54 0 34]
#[0 2 102 0 21 0 25 0 26 0 34 0 40 0 41 0 76]
#[0 2 50 0 21 0 25 0 26 0 76 0 79]
#[1 1 13 0 76 2 85 0 124 1 21 0 125]
#[1 2 89 0 17 2 30 0 21 2 30 0 82]
#[1 2 93 0 21 2 97 0 82] )

16. ID ::= letter { letter | digit } ;
a..z a..z
0..9

17. id := #letter , (#letter / #digit) star
sequence
letter star
choice
letter digit

18. id := #letter asParser ,
(#letter asParser / #digit asParser) star
sequence
letter star
choice
letter digit

19. Scannerless Parser

20. Parsing Expression
Grammar

21. Packrat Parser

22. Parser Combinator

24. Grammar
Transformation

25. Graph
Rewriting

26. #letter → #letter / $_
sequence
letter star
choice
letter digit

27. #letter → #letter / $_
sequence
choice star
letter _ choice
choice digit
letter _

28. Optimizations

29. (`a / `b) / `c → `a / `b / `c
sequence
choice star
letter _ choice
choice digit
letter _

30. (`a / `b) / `c → `a / `b / `c
sequence
choice star
letter _ choice
letter _ digit

31. (`a / `b) / `c → `a / `b / `c
in general sequence
a graph
choice star
letter _ choice
letter _ digit

32. Conflicts?

33. SELECT * FROM users

34. |r|
r := SELECT * FROM users .
^ User fromRow: r

35. expr | sql

36. <SQL: SELECT * FROM users>

37. ordered
expr / sql

38. No Conflicts

39. No Ambiguities

40. surprise
expr / sql

41. surprise
sql / expr

42. !expr sql / !sql expr
expr | sql

43. !expr sql / !sql expr / ui
expr $ sql