Practical, General Parser Combinators

Presented at PEPM '16 in St. Petersburg, FL, January 2016.

Event link:
http://conf.researchr.org/track/POPL-2016/pepm-2016-main#program

Meerkat parsers: http://meerkat-parser.github.io/

Transcript

1. Practical, General Parser Combinators Anastasia Izmaylova, Ali Afroozeh and Tijs van der Storm
2. Trade-offs Flexibility Expressivity Performance
3. Performance Compiler construction DSLs Reverse Engineering Speed Natural grammars Modularity
4. Performance Compiler construction DSLs Reverse Engineering Speed Natural grammars Modularity
5. Performance Compiler construction DSLs Reverse Engineering Speed Natural grammars Modularity General parsing technology
6. Performance O(n) O(n3) Deterministic Highly Ambiguous
9. E ::= '-' E | E '*' E | E '+' E | Num '*' > '+' Expressivity
10. E ::= '-' E | E '*' E | E '+' E | Num E ::= E '+' T | T T ::= T '*' F | F F ::= '-' F | Num '*' > '+' Expressivity
11. E ::= '-' E | E '*' E | E '+' E | Num E ::= E '+' T | T T ::= T '*' F | F F ::= '-' F | Num E ::= T E1 E1 ::= '+' T E1 | ε T ::= F T1 T1 ::= '*' F | ε F ::= '-' F | Num '*' > '+' Expressivity
12. E ::= '-' E | E '*' E | E '+' E | Num E ::= E '+' T | T T ::= T '*' F | F F ::= '-' F | Num E ::= T E1 E1 ::= '+' T E1 | ε T ::= F T1 T1 ::= '*' F | ε F ::= '-' F | Num '*' > '+' Expressivity
13. E ::= '-' E | E '*' E | E '+' E | Num E ::= E '+' T | T T ::= T '*' F | F F ::= '-' F | Num E ::= T E1 E1 ::= '+' T E1 | ε T ::= F T1 T1 ::= '*' F | ε F ::= '-' F | Num '*' > '+' Expressivity
14. E ::= '-' E | E '*' E | E '+' E | Num E ::= E '+' T | T T ::= T '*' F | F F ::= '-' F | Num E ::= T E1 E1 ::= '+' T E1 | ε T ::= F T1 T1 ::= '*' F | ε F ::= '-' F | Num '*' > '+' Expressivity
15. Flexibility def Primary = ( PrimaryNoNewArray | ArrayCreationExpression ) def PrimaryNoNewArray = ( Literal | Type ~ "." ~ "class" | "void" ~ "." ~ "class" | "this" | ClassName ~ "." ~ "this" | "(" ~ Expression ~ ")" | ClassInstanceCreationExpression | FieldAccess | MethodInvocation | ArrayAccess ) def Literal = ( IntegerLiteral | FloatingPointLiteral | BooleanLiteral | CharacterLiteral | StringLiteral | NullLiteral ) primary : '(' primaryNoNewArray ')'
 | arrayCreationExpression
 ; 
 primaryNoNewArray : literal
 | type '.' 'class' | 'void' '.' 'class' | 'this' | className '.' 'this' | '(' type ')' | '(' expression ')' | classInstanceCreationExpression | fieldAccess | methodInvocation | arrayAccess
 ; literal : integerLiteral
 | floatingPointLiteral | booleanLiteral | characterLiteral | stringLiteral | nullLiteral
 ;
16. General top-down parsing
18. Recursive-descent parsing
19. Recursive-descent parsing Memoization in CFGs Norvig 91
20. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91
21. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 LR Parsing Knuth 65
22. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65
23. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85
24. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85 RNGLR Parsing Scott and Johnstone 06
25. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85 RNGLR Parsing Scott and Johnstone 06 GLR with reduced stack Aycock and Horspool 99
26. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85 RNGLR Parsing Scott and Johnstone 06 GLR with reduced stack Aycock and Horspool 99 RIGLR Scott and Johnstone 05
27. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85 RNGLR Parsing Scott and Johnstone 06 GLR with reduced stack Aycock and Horspool 99 RIGLR Scott and Johnstone 05 GLL Parsing Scott and Johnstone 13
28. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85 RNGLR Parsing Scott and Johnstone 06 GLR with reduced stack Aycock and Horspool 99 RIGLR Scott and Johnstone 05 GLL Parsing Scott and Johnstone 13 GLL parsing with a different GSS Afroozeh and Izmaylova 15
29. Recursive-descent parsing Memoization in CFGs Norvig 91 Memoization in CPS Johnson 91 Recursive-ascent parsing Penello 86 LR Parsing Knuth 65 GLR Parsing Tomita 85 RNGLR Parsing Scott and Johnstone 06 GLR with reduced stack Aycock and Horspool 99 RIGLR Scott and Johnstone 05 GLL Parsing Scott and Johnstone 13 GLL parsing with a different GSS Afroozeh and Izmaylova 15 This work
31. Basic RD recognizers
32. Basic RD recognizers Memorized CPS recognizers Memorization in top-down parsing Johnson '91
33. Basic RD recognizers Cubic CPS recognizers Memorized CPS recognizers Memorization in top-down parsing Johnson '91
34. Basic RD recognizers Cubic CPS recognizers Binarized SPPFs Memorized CPS recognizers Memorization in top-down parsing Johnson '91 BRNGLR, Scott & Johnstone ’07 GLL Parsing, Scott & Johnstone '13
35. Basic RD recognizers Cubic CPS recognizers Binarized SPPFs Memorized CPS recognizers Memorization in top-down parsing Johnson '91 BRNGLR, Scott & Johnstone ’07 GLL Parsing, Scott & Johnstone '13 Cubic CPS parsers
36. Basic recursive-descent recognizers type Result[T] = Option[T]
 def success[T](t: T) = Some(t)
 def failure[T] = None
37. Basic recursive-descent recognizers type Result[T] = Option[T]
 def success[T](t: T) = Some(t)
 def failure[T] = None type Recognizer = Int => Result[Int]

38. Basic recursive-descent recognizers type Result[T] = Option[T]
 def success[T](t: T) = Some(t)
 def failure[T] = None type Recognizer = Int => Result[Int]
 def epsilon: Recognizer =
 i => success(i)
39. Basic recursive-descent recognizers type Result[T] = Option[T]
 def success[T](t: T) = Some(t)
 def failure[T] = None type Recognizer = Int => Result[Int]
 def epsilon: Recognizer =
 i => success(i) def terminal(t: String): Recognizer =
 i => if(input.startsWith(t, i)) success(i + t.length) else failure
40. Basic recursive-descent recognizers type Result[T] = Option[T]
 def success[T](t: T) = Some(t)
 def failure[T] = None type Recognizer = Int => Result[Int]
 def epsilon: Recognizer =
 i => success(i) def terminal(t: String): Recognizer =
 i => if(input.startsWith(t, i)) success(i + t.length) else failure def seq(rs: Recognizer*): Recognizer =
 rs.reduceLeft((cur, r) => (i => cur(i).flatMap(r)))
41. Basic recursive-descent recognizers type Result[T] = Option[T]
 def success[T](t: T) = Some(t)
 def failure[T] = None type Recognizer = Int => Result[Int]
 def epsilon: Recognizer =
 i => success(i) def terminal(t: String): Recognizer =
 i => if(input.startsWith(t, i)) success(i + t.length) else failure def seq(rs: Recognizer*): Recognizer =
 rs.reduceLeft((cur, r) => (i => cur(i).flatMap(r))) 
 
 
 
 
 
 def rule(nt: String, alts: Recognizer*): Recognizer =
 alts.reduce((cur, alt) => i => cur(i).orElse(alt(i)))
42. Full backtracking
43. Full backtracking trait MonadPlus[T, M[_] <: MonadPlus[_, M]] {
 def map[U](f: T => U): M[U]
 def flatMap[U](f: T => M[U]): M[U]
 def orElse(r: => M[T]): M[T]
 }
44. Full backtracking trait MonadPlus[T, M[_] <: MonadPlus[_, M]] {
 def map[U](f: T => U): M[U]
 def flatMap[U](f: T => M[U]): M[U]
 def orElse(r: => M[T]): M[T]
 } type Result[T] <: MonadPlus[T, Result]
45. Full backtracking trait MonadPlus[T, M[_] <: MonadPlus[_, M]] {
 def map[U](f: T => U): M[U]
 def flatMap[U](f: T => M[U]): M[U]
 def orElse(r: => M[T]): M[T]
 } type Result[T] <: MonadPlus[T, Result] type K[T] = T => Unit
 
 trait Result[T] extends (K[T] => Unit) with MonadPlus[T, Result]
46. Full backtracking r1 = i => k => if (input.charAt(i) == 'a') k(i+1) r2 = i => k => if (input.charAt(i) == 'b') k(i+1) k0: Int => Unit = println(“Success”) r1(i).flatMap(r2): i => k => r1(i)(j => r2(j)(k))
47. Left recursion & memoization
48. Left recursion & memoization def memo[T](f: Int => Result[T]): Int => Result[T] = {
 val table: Map[Int, Result[T]] = HashMap.empty
 i => table.getOrElseUpdate(i, memo_result(f(i)))
 }
49. Left recursion & memoization def memo[T](f: Int => Result[T]): Int => Result[T] = {
 val table: Map[Int, Result[T]] = HashMap.empty
 i => table.getOrElseUpdate(i, memo_result(f(i)))
 }
50. Left recursion & memoization def memo[T](f: Int => Result[T]): Int => Result[T] = {
 val table: Map[Int, Result[T]] = HashMap.empty
 i => table.getOrElseUpdate(i, memo_result(f(i)))
 } def memo_result[T](res: => Result[T]): Result[T] = {
 val Rs: MutableList[T] = MutableList.empty
 val Ks: MutableList[K[T]] = MutableList.empty
 return result(k =>
 if(Ks.isEmpty) {
 Ks += k
 val k_i: K[T] = t => if (!Rs.contains(t)) { 
 Rs += t; for(kt <- Ks) kt(t) 
 }
 res(k_i)
 } else {
 Ks += k
 for(t <- Rs) k(t)
 })
 }
51. Left recursion & memoization def memo[T](f: Int => Result[T]): Int => Result[T] = {
 val table: Map[Int, Result[T]] = HashMap.empty
 i => table.getOrElseUpdate(i, memo_result(f(i)))
 } def memo_result[T](res: => Result[T]): Result[T] = {
 val Rs: MutableList[T] = MutableList.empty
 val Ks: MutableList[K[T]] = MutableList.empty
 return result(k =>
 if(Ks.isEmpty) {
 Ks += k
 val k_i: K[T] = t => if (!Rs.contains(t)) { 
 Rs += t; for(kt <- Ks) kt(t) 
 }
 res(k_i)
 } else {
 Ks += k
 for(t <- Rs) k(t)
 })
 }
52. Left recursion & memoization def memo[T](f: Int => Result[T]): Int => Result[T] = {
 val table: Map[Int, Result[T]] = HashMap.empty
 i => table.getOrElseUpdate(i, memo_result(f(i)))
 } def memo_result[T](res: => Result[T]): Result[T] = {
 val Rs: MutableList[T] = MutableList.empty
 val Ks: MutableList[K[T]] = MutableList.empty
 return result(k =>
 if(Ks.isEmpty) {
 Ks += k
 val k_i: K[T] = t => if (!Rs.contains(t)) { 
 Rs += t; for(kt <- Ks) kt(t) 
 }
 res(k_i)
 } else {
 Ks += k
 for(t <- Rs) k(t)
 })
 }
53. Left recursion & memoization def memo[T](f: Int => Result[T]): Int => Result[T] = {
 val table: Map[Int, Result[T]] = HashMap.empty
 i => table.getOrElseUpdate(i, memo_result(f(i)))
 } def memo_result[T](res: => Result[T]): Result[T] = {
 val Rs: MutableList[T] = MutableList.empty
 val Ks: MutableList[K[T]] = MutableList.empty
 return result(k =>
 if(Ks.isEmpty) {
 Ks += k
 val k_i: K[T] = t => if (!Rs.contains(t)) { 
 Rs += t; for(kt <- Ks) kt(t) 
 }
 res(k_i)
 } else {
 Ks += k
 for(t <- Rs) k(t)
 })
 }
54. Memoization on continutations S ::= S S S | S S | b
55. Memoization on continutations S ::= S S S | S S | b Multiple calls at the same input position
56. Memoization on continutations S ::= S S S | S S | b Multiple calls at the same input position def memo_k[T](f: T => Unit): T => Unit = {
 val s: Set[T] = HashSet.empty
 return t => if(!s.contains(t)) { s += t; f(t) }
 }
57. S ::= a S b S | a S | s Input: aasb
58. S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 a (a) Parse tree 1 (b) Parse tree 2 S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 (a) Parse tree 1 (b) Parse tree 2 S ::= a S b S | a S | s Input: aasb
59. S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 a (a) Parse tree 1 (b) Parse tree 2 S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 (a) Parse tree 1 (b) Parse tree 2 , 0, 4 , 1, 3 b, 3, 4 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 a, 0, 1 S, 1, 3 a, 1, 2 S ::= a S . b, 0, 3 (S ::= aSb., 3) rse tree 1 (b) Parse tree 2 (c) SPPF (d) B S ::= a S b S | a S | s Input: aasb
60. S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 a (a) Parse tree 1 (b) Parse tree 2 S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 2, 3 s, 2, 3 a, 1, 2 b, 3, 4 (a) Parse tree 1 (b) Parse tree 2 S ::= a S b S | a S | s 4 3 b, 3, 4 S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S, 0, 4 a, 0, 1 S, 1, 3 b, 3, 4 a, 1, 2 S, 2, 3 s, 2, 3 S, 1, 4 S ::= a S . b, 0, 3 S ::= a S . b, 1, 3 (S ::= aSb., 3) (S ::= aS., 1) ee 2 (c) SPPF (d) Binarized SPPF Input: aasb
61. Cubic CPS parsers type Parser = Int => Result[SPPFNode]
62. Cubic CPS parsers type Parser = Int => Result[SPPFNode] def terminal(t: String): Parser = i => if(input.startsWith(t, i)) success(sppf.getTerminalNode(t, i, i + t.length)) else failure
 def epsilon: Parser = i => success(sppf.getEpsilonNode(i))
63. Cubic CPS parsers type Parser = Int => Result[SPPFNode] def terminal(t: String): Parser = i => if(input.startsWith(t, i)) success(sppf.getTerminalNode(t, i, i + t.length)) else failure
 def epsilon: Parser = i => success(sppf.getEpsilonNode(i)) def seq(ps: Parser*): Parser = ps.reduceLeft(seq2) def seq2(p1: Parser, p2: Parser) = fix(q => i => p1(i).flatMap(t1 => p2(t1.rightExtent).map(t2 => sppf.getIntermediateNode(q, t1, t2))))
64. Cubic CPS parsers type Parser = Int => Result[SPPFNode] def terminal(t: String): Parser = i => if(input.startsWith(t, i)) success(sppf.getTerminalNode(t, i, i + t.length)) else failure
 def epsilon: Parser = i => success(sppf.getEpsilonNode(i)) def seq(ps: Parser*): Parser = ps.reduceLeft(seq2) def seq2(p1: Parser, p2: Parser) = fix(q => i => p1(i).flatMap(t1 => p2(t1.rightExtent).map(t2 => sppf.getIntermediateNode(q, t1, t2)))) def rule(nt: String, alts: Parser*): Parser = alts.map(rule1(nt, _)).reduce((cur, p) => i => cur(i).orElse(p(i))) def rule1(nt: String, p: Parser): Parser = fix(q => i => p(i).map(t => sppf.getNonterminalNode(nt, q, t)))
65. Highly-ambiguous grammar 0 100 200 300 400 500 0 2000 6000 10000 Size (#characters) CPU time (ms) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • y = 0.000064 x3 + 0.0137 x2 − 2.8824 x 91.2971 R2 = 0.9998 Regression line S ::= SSS | SS | b
66. Pragmatics
67. Pragmatics • Lexical disambiguation filters
68. Pragmatics • Lexical disambiguation filters • Layout (whitespace/comment) insertion
69. Pragmatics • Lexical disambiguation filters • Layout (whitespace/comment) insertion • Semantic actions and terms
70. Pragmatics • Lexical disambiguation filters • Layout (whitespace/comment) insertion • Semantic actions and terms See our ScalaDays 2015 talk!
71. Java 3 4 5 0 1 2 3 Size (#characters) in log10 CPU time (ms) in log10 y = 1.138201 x − 8.696786 R2 = 0.9828 Regression line 7449 Java source files from JDK 1.7.0_60-b19
72. Operator Precedence val E: OperatorNonterminal = syn ( right{ E ~ "^" ~ E } |> "-" ~ E |> left ( E ~ "*" ~ E | E ~ "/" ~ E ) |> left ( E ~ "+" ~ E | E ~ "-" ~ E ) | "(" ~ E ~ ")" | "[0-9]".r )
73. val Primary: Nonterminal = syn ( PrimaryNoNewArray | ArrayCreationExpression ) val PrimaryNoNewArray: Nonterminal = syn ( Literal | Type ~ "." ~ "class" | "void" ~ "." ~ "class" | "this" | ClassName ~ "." ~ "this" | "(" ~ Expression ~ ")" | ClassInstanceCreationExpression | FieldAccess | MethodInvocation | ArrayAccess ) val Literal: Nonterminal = syn ( IntegerLiteral | FloatingPointLiteral | BooleanLiteral | CharacterLiteral | StringLiteral | NullLiteral ) val IntegerLiteral: Nonterminal = syn ( DecimalIntegerLiteral.!>>(".") | HexIntegerLiteral.!>>(".") | OctalIntegerLiteral | BinaryIntegerLiteral ) val FloatingPointLiteral: Nonterminal = syn ( DecimalFloatingPointLiteral | HexadecimalFloatingPointLiteral ) val ClassInstanceCreationExpression: Nonterminal = syn ( "new" ~ TypeArguments.? ~ TypeDeclSpecifier ~ TypeArguments | (Primary | QualifiedIdentifier).! ~ "." ~ "new" ~ TypeArgum ) val TypeArgumentsOrDiamond: Nonterminal = syn ( "<" ~ ">" | TypeArguments ) val ArgumentList: Nonterminal = syn (Expression.+(",")) val ArrayCreationExpression: Nonterminal = syn ( "new" ~ (PrimitiveType | ReferenceType).! ~ DimExpr.+ ~ ("[ val Expression: OperatorNonterminal = syn ( Expression ~ "." ~ Identifier | Expression ~ "." ~ "this" | Expression ~ "." ~ "new" ~ TypeArguments.? ~ Identifier ~ TypeArgumentsOrDiamond.? ~ "(" ~ ArgumentList.? ~ ")" ~ ClassBody.? | Expression ~ "." ~ NonWildTypeArguments ~ ExplicitGenericInvocationSuffix | Expression ~ "." ~ "super" ~ ("." ~ Identifier).!.? ~ Arguments | Type ~ "." ~ "class" | "void" ~ "." ~ "class" | Expression ~ "(" ~ ArgumentList.? ~ ")" | Expression ~ "[" ~ Expression ~ "]" |> Expression ~ "++" | Expression ~ "--" |> "+".!>>("+") ~ Expression | "-".!>>("-") ~ Expression | "++" ~ Expression | "--" ~ Expression | "!" ~ Expression | "~" ~ Expression | "new" ~ ClassInstanceCreationExpression | "new" ~ ArrayCreationExpression | "(" ~ PrimitiveType ~ ")" ~ Expression | "(" ~ ReferenceType ~ ")" ~ Expression |> left ( Expression ~ "*" ~ Expression | Expression ~ "/" ~ Expression | Expression ~ "%" ~ Expression ) |> left ( Expression ~ "+".!>>("+") ~ Expression | Expression ~ "-".!>>("-") ~ Expression ) |> left ( Expression ~ "<<" ~ Expression | Expression ~ ">>".!>>(">") ~ Expression | Expression ~ ">>>" ~ Expression ) |> left ( Expression ~ "<".!>>("[=<]".r) ~ Expression | Expression ~ ">".!>>("[=>]".r) ~ Expression | Expression ~ "<=" ~ Expression | Expression ~ ">=" ~ Expression | Expression ~ "instanceof" ~ Type ) |> left ( Expression ~ "==" ~ Expression | Expression ~ "!=" ~ Expression ) |> Expression ~ "&".!>>("&") ~ Expression |> Expression ~ "^" ~ Expression |> Expression ~ "|".!>>("|") ~ Expression |> Expression ~ "&&" ~ Expression |> Expression ~ "||" ~ Expression |> Expression ~ "?" ~ Expression ~ ":" ~ Expression |> Expression ~ AssignmentOperator ~ Expression | "(" ~ Expression ~ ")" | Primary)
74. ) val InclusiveOrExpression: Nonterminal = syn ( ExclusiveOrExpression | InclusiveOrExpression ~ "|" ~ ExclusiveOrExpression ) val ConditionalAndExpression: Nonterminal = syn ( InclusiveOrExpression | ConditionalAndExpression ~ "&&" ~ InclusiveOrExpression ) val ConditionalOrExpression: Nonterminal = syn ( ConditionalAndExpression | ConditionalOrExpression ~ "||" ~ ConditionalAndExpression ) val ConditionalExpression: Nonterminal = syn ( ConditionalOrExpression | ConditionalOrExpression ~ "?" ~ Expression ~ ":" ~ Conditio ) val AssignmentExpression: Nonterminal = syn ( ConditionalExpression | Assignment ) val Assignment: Nonterminal = syn ( LeftHandSide ~ AssignmentOperator ~ AssignmentExpression ) val LeftHandSide: Nonterminal = syn ( ExpressionName | "(" ~ LeftHandSide ~ ")" | FieldAccess | ArrayAccess ) val AssignmentOperator: Nonterminal = syn ( "=" | "+=" | "-=" | "*=" | "/=" | "&=" | "|=" | "^=" | "%=" | "<<=" | ">>=" | ">>>=" ) val Expression: Nonterminal = syn ( AssignmentExpression ) val Expression: OperatorNonterminal = syn ( Expression ~ "." ~ Identifier | Expression ~ "." ~ "this" | Expression ~ "." ~ "new" ~ TypeArguments.? ~ Identifier ~ TypeArgumentsOrDiamond.? ~ "(" ~ ArgumentList.? ~ ")" ~ ClassBody.? | Expression ~ "." ~ NonWildTypeArguments ~ ExplicitGenericInvocationSuffix | Expression ~ "." ~ "super" ~ ("." ~ Identifier).!.? ~ Arguments | Type ~ "." ~ "class" | "void" ~ "." ~ "class" | Expression ~ "(" ~ ArgumentList.? ~ ")" | Expression ~ "[" ~ Expression ~ "]" |> Expression ~ "++" | Expression ~ "--" |> "+".!>>("+") ~ Expression | "-".!>>("-") ~ Expression | "++" ~ Expression | "--" ~ Expression | "!" ~ Expression | "~" ~ Expression | "new" ~ ClassInstanceCreationExpression | "new" ~ ArrayCreationExpression | "(" ~ PrimitiveType ~ ")" ~ Expression | "(" ~ ReferenceType ~ ")" ~ Expression |> left ( Expression ~ "*" ~ Expression | Expression ~ "/" ~ Expression | Expression ~ "%" ~ Expression ) |> left ( Expression ~ "+".!>>("+") ~ Expression | Expression ~ "-".!>>("-") ~ Expression ) |> left ( Expression ~ "<<" ~ Expression | Expression ~ ">>".!>>(">") ~ Expression | Expression ~ ">>>" ~ Expression ) |> left ( Expression ~ "<".!>>("[=<]".r) ~ Expression | Expression ~ ">".!>>("[=>]".r) ~ Expression | Expression ~ "<=" ~ Expression | Expression ~ ">=" ~ Expression | Expression ~ "instanceof" ~ Type ) |> left ( Expression ~ "==" ~ Expression | Expression ~ "!=" ~ Expression ) |> Expression ~ "&".!>>("&") ~ Expression |> Expression ~ "^" ~ Expression |> Expression ~ "|".!>>("|") ~ Expression |> Expression ~ "&&" ~ Expression |> Expression ~ "||" ~ Expression |> Expression ~ "?" ~ Expression ~ ":" ~ Expression |> Expression ~ AssignmentOperator ~ Expression | "(" ~ Expression ~ ")" | Primary)
75. Meerkat Parsers Anastasia Izmaylova @IAnastassija & Ali Afroozeh @afruze https://github.com/meerkat-parser