Compiler Components and their Generators - LR Parsing

1. Compiler Components & Generators Traditional Parsing Algorithms Guido Wachsmuth Delft Course IN4303 University of Technology Compiler Construction Challenge the future

2. Recap: Traditional Parsing Algorithms lessons learned How can we parse context-free languages effectively? • predictive parsing algorithms • LR parsing algorithms Which grammar classes are supported by these algorithms? • LL(k) grammars, LL(k) languages • LR(k) grammars, LR(k) languages How can we generate compiler tools from that? • implement automata • generate parse tables Traditional Parsing Algorithms 2

3. Overview today’s lecture Lexical Analysis 3

4. Overview today’s lecture efficient parsing algorithms • LR parse table generation • SLR & LALR parse tables Lexical Analysis 3

5. Overview today’s lecture efficient parsing algorithms • LR parse table generation • SLR & LALR parse tables plagues of traditional parsing algorithms • paradise lost • paradise regained Lexical Analysis 3

6. I LR parse tables Lexical Analysis 4

7. Recap: LR parsing example stack input $ 7 * 3 + 7 * 3 $ Traditional Parsing Algorithms 5

8. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ Traditional Parsing Algorithms 5

9. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ Traditional Parsing Algorithms 5

10. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ Traditional Parsing Algorithms 5

13. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ Traditional Parsing Algorithms 5

14. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ Traditional Parsing Algorithms 5

17. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ $ E + E * 3 $ Traditional Parsing Algorithms 5

20. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ $ E + E * 3 $ $ E + E * E $ Traditional Parsing Algorithms 5

21. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ $ E + E * 3 $ $ E + E * E $ $ E + E $ Traditional Parsing Algorithms 5

22. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ $ E + E * 3 $ $ E + E * E $ $ E + E $ $ E $ Traditional Parsing Algorithms 5

23. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ $ E + E * 3 $ $ E + E * E $ $ E + E $ $ E $ Traditional Parsing Algorithms 5

24. Recap: LR parsing example $ 7 * 3 + 7 * 3 $ $ E * 3 + 7 * 3 $ $ E * E + 7 * 3 $ $ E + 7 * 3 $ $ E + E * 3 $ $ E + E * E $ $ E + E $ $ E $ $ S Traditional Parsing Algorithms 5

25. Recap: LR parsing parse table rows T1 ... N1 ... • states of a DFA 1 s3 2 a g5 columns 3 r1 • topmost stack symbol, Σ, N 4 r2 entries 5 • reduce, rule number 6 g1 • shift, goto state 7 s1 • goto state 8 • accept ... Traditional Parsing Algorithms 6

26. LR(0) parse tables items, closure & goto S→x S→(L) L→S L→L,S Traditional Parsing Algorithms 7

27. LR(0) parse tables items, closure & goto S’ → . S $ S→x S→(L) L→S L→L,S Traditional Parsing Algorithms 7

28. LR(0) parse tables items, closure & goto item S’ → . S $ S→x S→(L) L→S L→L,S Traditional Parsing Algorithms 7

29. LR(0) parse tables items, closure & goto item closure • for every item A → α . X β S’ → . S $ • for every rule X → γ • add item X → . γ S→x S→(L) L→S L→L,S Traditional Parsing Algorithms 7

30. LR(0) parse tables items, closure & goto closure • for every item A → α . X β S’ → . S $ S→.x • for every rule X → γ S→.(L) • add item X → . γ S→x S→(L) L→S L→L,S Traditional Parsing Algorithms 7

31. LR(0) parse tables items, closure & goto S’ → . S $ S→.x S→.(L) S→x S→(L) L→S L→L,S Traditional Parsing Algorithms 7

32. LR(0) parse tables items, closure & goto S’ → . S $ S→.x S→.(L) S S→x S→(L) L→S L→L,S S’ → S . $ Traditional Parsing Algorithms 7

33. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x S→.(L) S S→x S→(L) L→S L→L,S S’ → S . $ Traditional Parsing Algorithms 7

34. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x S→.(L) ( S→(.L) S S→x S→(L) L→S L→L,S S’ → S . $ Traditional Parsing Algorithms 7

35. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x S→.(L) ( S→(.L) L→.S L→.L,S S→.x S→x S S→.(L) S→(L) L→S L→L,S S’ → S . $ Traditional Parsing Algorithms 7

36. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x x S→.(L) ( S→(.L) L→.S L→.L,S S→.x S→x S S→.(L) S→(L) L→S L→L,S S’ → S . $ Traditional Parsing Algorithms 7

37. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x x S→.(L) ( S→(.L) L→.S L→.L,S ( S→.x S S→x S→.(L) S→(L) L→S L→L,S S’ → S . $ Traditional Parsing Algorithms 7

38. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x x S→.(L) ( S→(.L) L→.S L→.L,S ( S→.x S S→x S→.(L) S→(L) S L→S L→L,S S’ → S . $ L→S. Traditional Parsing Algorithms 7

39. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x x S→.(L) ( S→(.L) L→.S L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S L→S L→L,S S’ → S . $ L→S. Traditional Parsing Algorithms 7

40. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x x S→.(L) ( S→(.L) L→.S L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ L→S. S→(L). Traditional Parsing Algorithms 7

41. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ S→.x x S→.(L) ( L→L,.S S→(.L) L→.S , L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ L→S. S→(L). Traditional Parsing Algorithms 7

42. LR(0) parse tables items, closure & goto x S→x. S’ → . S $ L→L,.S S→.x x S→.x S→.(L) ( S→.(L) S→(.L) L→.S , L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ L→S. S→(L). Traditional Parsing Algorithms 7

43. LR(0) parse tables items, closure & goto x x S→x. S’ → . S $ L→L,.S S→.x x S→.x S→.(L) ( S→.(L) S→(.L) L→.S , L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ L→S. S→(L). Traditional Parsing Algorithms 7

44. LR(0) parse tables items, closure & goto x x S→x. S’ → . S $ L→L,.S S→.x x S→.x S→.(L) ( ( S→.(L) S→(.L) L→.S , L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ L→S. S→(L). Traditional Parsing Algorithms 7

45. LR(0) parse tables items, closure & goto L→L,S. S x x S→x. S’ → . S $ L→L,.S S→.x x S→.x S→.(L) ( ( S→.(L) S→(.L) L→.S , L→.L,S ( S→.x S L S→(L.) S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ L→S. S→(L). Traditional Parsing Algorithms 7

46. LR(0) parse tables items, closure & goto L→L,S.9 S x x S→x. 2 S’ → . S $ 1 L→L,.S8 S→.x x S→.x S→.(L) ( ( S→.(L) S→(.L)3 L→.S , L→.L,S ( S→.x S L S→(L.)5 S→x S→.(L) L→L.,S S→(L) S ) L→S L→L,S S’ → S . $ 4 L→S. 6 S→(L).7 Traditional Parsing Algorithms 7

47. LR(0) parse tables result ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 7 r2 r2 r2 r2 r2 L→L,S 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

48. LR(0) parse tables result ( x , x ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

49. LR(0) parse tables result x , x ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

50. LR(0) parse tables result , x ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) 2 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

51. LR(0) parse tables result , x ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

53. LR(0) parse tables result , x ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

55. LR(0) parse tables result x ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 8 S→x 6 r3 r3 r3 r3 r3 S→(L) 5 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

56. LR(0) parse tables result ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 2 5 s7 s8 8 S→x 6 r3 r3 r3 r3 r3 S→(L) 5 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

57. LR(0) parse tables result ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 8 S→x 6 r3 r3 r3 r3 r3 S→(L) 5 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

58. LR(0) parse tables result ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 9 5 s7 s8 8 S→x 6 r3 r3 r3 r3 r3 S→(L) 5 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

59. LR(0) parse tables result ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

60. LR(0) parse tables result ) $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) 5 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

61. LR(0) parse tables result $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 7 S→x 6 r3 r3 r3 r3 r3 S→(L) 5 L→S 3 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

62. LR(0) parse tables result $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

63. LR(0) parse tables result $ ( ) x , $ S L 1 s3 s2 g4 2 r1 r1 r1 r1 r1 3 s3 s2 g6 g5 4 a 5 s7 s8 S→x 6 r3 r3 r3 r3 r3 S→(L) L→S 4 7 r2 r2 r2 r2 r2 L→L,S 1 8 s3 s2 g9 9 r4 r4 r4 r4 r4 Traditional Parsing Algorithms 8

64. SLR parse tables shift-reduce conflicts E S→E.$ S→.E$ E→.T+E E→.T T E→T.+E T→.x E→T. T + x E→T+.E E→.T+E E→T+E E→.T E→T T→x. x T→.x E E→T+E. T→x Traditional Parsing Algorithms 9

65. SLR parse tables shift-reduce conflicts E S→E.$ 2 S→.E$ E→.T+E E→.T T E→T.+E T→.x 1 E→T. 3 T + x E→T+.E E→.T+E E→T+E E→.T E→T T→x. x T→.x E E→T+E. 6 5 4 T→x Traditional Parsing Algorithms 9

66. SLR parse tables shift-reduce conflicts x + $ E T 1 s5 g2 g3 E S→E.$ 2 2 a S→.E$ E→.T+E 3 r2 ? r2 E→.T T 4 s5 g6 g3 E→T.+E T→.x 1 5 r3 r3 r3 E→T. 3 6 r1 r1 r1 T + x E→T+.E E→.T+E E→T+E E→.T E→T T→x. x T→.x E E→T+E. 6 5 4 T→x Traditional Parsing Algorithms 9

67. SLR parse tables shift-reduce conflicts x + $ E T 1 s5 g2 g3 E S→E.$ 2 2 a S→.E$ E→.T+E 3 s4 r2 E→.T T 4 s5 g6 g3 E→T.+E T→.x 1 5 r3 r3 E→T. 3 6 r1 T + x E→T+.E E→.T+E E→T+E E→.T E→T T→x. x T→.x E E→T+E. 6 5 4 T→x Traditional Parsing Algorithms 9

68. LR(1) parse tables look-ahead E S→E.$ ? S→.E$ ? E→.T+E $ E→.T $ T E→T.+E $ T→.x +$ E→T. $ T + x E→T+.E $ E→.T+E $ E→T+E E→.T $ E→T T→x. +$ x T→.x +$ E E→T+E. $ T→x Traditional Parsing Algorithms 10

69. LR(1) parse tables look-ahead x + $ E T 1 s5 g2 g3 E S→E.$ ? 2 a S→.E$ ? E→.T+E $ 3 s4 r2 E→.T $ T 4 s5 g6 g3 E→T.+E $ T→.x +$ 5 r3 r3 E→T. $ 6 r1 T + x E→T+.E $ E→.T+E $ E→T+E E→.T $ E→T T→x. +$ x T→.x +$ E E→T+E. $ T→x Traditional Parsing Algorithms 10

70. LALR(1) parse tables state space reduction unify states • with same items • and same outgoing transitions • but different look-ahead sets might introduce new conflicts Traditional Parsing Algorithms 11

71. coffee break Traditional Parsing Algorithms 12

72. II paradise lost & regained Lexical Analysis 13

73. PARADISE LOST

74. EFFICIENCY

75. THE FIRST PLAGUE WERE GRAMMAR CLASSES

76. context-free grammars

77. context-free grammars LL(0)

78. context-free grammars LL(1) LL(0)

79. context-free grammars LL(k) LL(1) LL(0)

80. context-free grammars LL(k) LL(1) LL(0) LR(0)

81. context-free grammars LL(k) LL(1) LR(1) LL(0) LR(0)

82. context-free grammars LL(k) LR(k) LL(1) LR(1) LL(0) LR(0)

83. context-free grammars LL(k) LR(k) LL(1) LR(1) SLR LL(0) LR(0)

84. context-free grammars LL(k) LR(k) LL(1) LR(1) LALR(1) SLR LL(0) LR(0)

85. Exp “+” Exp ➝ Exp Term (“+” Term)* ➝ Exp Exp “*” Exp ➝ Exp Fact (“*” Fact)* ➝ Term Num ➝ Exp Num ➝ Fact paradise grammar classes

86. Exp * Exp * Exp Term Term Term Exp Exp Exp Fact Fact Fact 3 + 7 + 21 3 + 7 + 21 paradise grammar classes

87. THE SECOND PLAGUE WAS DISAMBIGUATION

88. Exp Exp Exp Exp Exp Exp Exp Exp Exp Exp 3 * 7 + 21 3 * 7 + 21

89. precedence operators associativity 1 ( ), [ ] non-associative 2 new non-associative 3 . left-associative 4 ++, -- non-associative 5 -, +, !, ~, ++, --, (type) right-associative 6 *, /, % left-associative 7 +, - left-associative … … … text books

91. context-free grammars unambigous LL(k) LR(k) LL(1) LR(1) LALR(1) SLR LL(0) LR(0)

92. Exp “+” Term ➝ Exp Term ➝ Exp Term “*” Fact ➝ Term Fact ➝ Term Num ➝ Fact grammar classes

93. FALSE PROPHETS

94. L = {ab, a} L = {ab, a} “a” “b” ➝ A “a” “b” / “a” ➝ A “a” ➝A paradise PEGs

95. L = {ab, a} L = {a} “a” ➝ A “a” / “a” “b” ➝ A “a” “b” ➝ A paradise PEGs

96. if c1 then if c2 then s1 else s2 dangling else

97. “if ” E “then” S “else” S / “if ” E “then” S / “if ” E “then” S ➝S “if ” E “then” S “else” S ➝ S PEGs

98. THE THIRD PLAGUE WAS LEXICAL SYNTAX

99. morphology & syntax

100. LL(k) LR(k) LL(1) LR(1) LALR(1) SLR LL(0) LR(0) limited look-ahead

101. scanners

102. 3 * 7 + 21

103. 3 * 7 + 21

104. parsers

105. 3 * 7 + 21

106. Exp Exp Exp Exp Exp 3 * 7 + 21

107. x = 1. * .10 y : array [ 1 .. 10 ] of integer

108. x = 1. * .10 y : array [ 1 .. 10 ] of integer

109. x = 1. * .10 y : array [ 1. .10 ] of integer

110. THE FOURTH PLAGUE WAS TREE CONSTRUCTION

111. Exp Add Exp Add Exp Exp Exp Const Const Const 3 + 7 + 21 3 7 21 paradise

112. Exp * Add * Add Term Term Term Const Const Const Fact Fact Fact 3 7 21 3 + 7 + 21 grammar classes

113. expr: INTEGER { $$ = con($1); } | expr '+' expr { $$ = opr('+', 2, $1, $3);} | expr '*' expr { $$ = opr('*', 2, $1, $3);} ; semantic actions

114. THE FIFTH PLAGUE WAS EVOLUTION

115. Exp “+” Term ➝ Exp Exp “+” Exp ➝ Exp Term ➝ Exp Exp “*” Exp ➝ Exp Term “*” Fact ➝ Term Num ➝ Exp Fact ➝ Term Num ➝ Fact paradise grammar classes

116. CExp “+” Term ➝ CExp Term ➝ CExp Exp “+” Exp ➝ Exp Term “*” Fact ➝ Term Exp “*” Exp ➝ Exp Fact ➝ Term Num ➝ Exp Num ➝ Fact Exp “=” Exp ➝ Exp Exp “=” CExp ➝ Exp Exp “<” Exp ➝ Exp Exp “<” CExp ➝ Exp Exp “>” Exp ➝ Exp Exp “>” CExp ➝ Exp CExp ➝ Exp paradise grammar classes

117. THE SIXTH PLAGUE WAS COMPOSITION

118. parsers

123. scanners

124. public boolean authenticate(String user, String pw) { SQL stm = <| SELECT id FROM Users WHERE name = ${user} AND password = ${pw} |>; return executeQuery(stm).size() != 0; }

125. THE SEVENTH PLAGUE WAS RESTRICTION TO PARSERS

126. PRETTY PRINTERS

127. SENTENCE GENERATORS

128. AST ACCESS

129. IDE SUPPORT

130. PARADISE REGAINED

131. GENERALISED PARSING

134. context-free syntax Exp “+” Exp ➝ Exp Exp “*” Exp ➝ Exp Exp "+" Exp -> Exp Num ➝ Exp Exp "*" Exp -> Exp NUM -> Exp paradise SDF

135. DECLARATIVE DISAMBIGUATION

136. context-free grammars unambigous LL(k) LR(k) LL(1) LR(1) LALR(1) SLR LL(0) LR(0)

137. context-free grammars unambigous

139. precedence operators associativity 1 ( ), [ ] non-associative 2 new non-associative 3 . left-associative 4 ++, -- non-associative 5 -, +, !, ~, ++, --, (type) right-associative 6 *, /, % left-associative 7 +, - left-associative … … … text books

140. context-free priorities Exp "*" Exp -> Exp {left} > Exp "+" Exp -> Exp {left}

141. context-free syntax "if" E "then" S -> S {prefer} "if" E "then" S "else" S -> S

142. SCANNERLESS PARSING

143. morphology & syntax

144. lexical syntax [0-9]+ -> NUM [ tn] -> LAYOUT "//" ~[n]* [n] -> LAYOUT

145. parser

146. parser

147. DECLARATIVE TREE CONSTRUCTION

148. Exp Add Exp Add Exp Exp Exp Const Const Const 3 + 7 + 21 3 7 21 paradise

149. context-free syntax Exp "+" Exp -> Exp {cons("Add")} Exp "*" Exp -> Exp {cons("Mul")} NUM -> Exp {cons("Const")} SDF

150. Add Add( Add( Add Const("3"), Const("7") Const Const Const ), Const("21") 3 7 21 ) paradise SDF

151. SEAMLESS EVOLUTION

152. context-free syntax Exp "+" Exp -> Exp {cons("Add")} Exp "*" Exp -> Exp {cons("Mul")} NUM -> Exp {cons("Const")} Exp "=" Exp -> Exp {cons("Eq")} Exp ">" Exp -> Exp {cons("Gt")} Exp "<" Exp -> Exp {cons("Lt")}

153. MODULAR COMPOSITION

156. public boolean authenticate(String user, String pw) { SQL stm = <| SELECT id FROM Users WHERE name = ${user} AND password = ${pw} |>; return executeQuery(stm).size() != 0; }

157. module Java-SQL imports Java SQL exports context-free syntax "<|" Query "|>" -> Exp {cons("ToSQL")} "${" Exp "}" -> SqlExp {cons("FromSQL")}

158. BEYOND PARSERS

159. PRETTY PRINTERS

160. SENTENCE GENERATORS

161. AST ACCESS

162. IDE SUPPORT

163. III summary Lexical Analysis 88

164. Summary lessons learned Traditional Parsing Algorithms 89

165. Summary lessons learned How can we generate LR parse tables? • items, closure, goto Traditional Parsing Algorithms 89

166. Summary lessons learned How can we generate LR parse tables? • items, closure, goto How can we improve LR(0) parse table generation? • SLR: consider FOLLOW sets to avoid shift-reduce conflicts • LR(1): consider look-ahead in states • LALR(1): unify LR(1) states to reduce state space Traditional Parsing Algorithms 89

167. Summary lessons learned How can we generate LR parse tables? • items, closure, goto How can we improve LR(0) parse table generation? • SLR: consider FOLLOW sets to avoid shift-reduce conflicts • LR(1): consider look-ahead in states • LALR(1): unify LR(1) states to reduce state space Why are efficient parsing algorithms problematic? • not longer pure, declarative, beautiful • paradise lost: seven plagues • paradise regained: scannerless generalised parsing Traditional Parsing Algorithms 89

168. Summary lessons learned How can we generate LR parse tables? • items, closure, goto How can we improve LR(0) parse table generation? • SLR: consider FOLLOW sets to avoid shift-reduce conflicts • LR(1): consider look-ahead in states • LALR(1): unify LR(1) states to reduce state space Why are efficient parsing algorithms problematic? • not longer pure, declarative, beautiful • paradise lost: seven plagues • paradise regained: scannerless generalised parsing Traditional Parsing Algorithms 89

169. Literature learn more Traditional Parsing Algorithms 90

170. Literature learn more syntactical analysis Andrew W. Appel, Jens Palsberg: Modern Compiler Implementation in Java, 2nd edition. 2002 Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman, Monica S. Lam: Compilers: Principles, Techniques, and Tools, 2nd edition. 2006 Traditional Parsing Algorithms 90

171. Literature learn more syntactical analysis Andrew W. Appel, Jens Palsberg: Modern Compiler Implementation in Java, 2nd edition. 2002 Alfred V. Aho, Ravi Sethi, Jeffrey D. Ullman, Monica S. Lam: Compilers: Principles, Techniques, and Tools, 2nd edition. 2006 generalised parsing Eelco Visser: Syntax Definition for Language Prototyping. PhD thesis 1997 M.G.J. van den Brand, J. Scheerder, J.J. Vinju, and E. Visser: Disambiguation Filters for Scannerless Generalized LR Parsers. CC 2002 Lennart C. L. Kats, Eelco Visser, Guido Wachsmuth: Pure and Declarative Syntax Definition - Paradise Lost and Regained. SPLASH 2010 Traditional Parsing Algorithms 90

172. Outlook coming next lectures • Lecture 14: Beyond grammarware Question & Answer Jan 5 • 10 questions, submit & vote Lab Dec 10 • support expressions • support statements • support ordinary classes & fields Traditional Parsing Algorithms 91

173. questions Lexical Analysis 92

174. credits Lexical Analysis 93

175. Pictures copyrights Slide 1: Book Scanner by Ben Woosley, some rights reserved Slide 12: West Cornwall Pasty Co. by Dominica Williamson, some rights reserved Slide 91: Ostsee by Mario Thiel, some rights reserved Slide 92: Questions by Oberazzi, some rights reserved Slide 93: Too Much Credit by Andres Rueda, some rights reserved Slides 14-87: Pure and Declarative Syntax Definition: Paradise Lost and Regained, some rights reserved Traditional Parsing Algorithms 94

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