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| 1 part of petitparser; | |
| 2 | |
| 3 /// Helper to conveniently define and build complex, recursive grammars using | |
| 4 /// plain Dart code. | |
| 5 /// | |
| 6 /// To create a new grammar definition subclass [GrammarDefinition]. For every | |
| 7 /// production create a new method returning the primitive parser defining it. | |
| 8 /// The method called [start] is supposed to return the start production of the | |
| 9 /// grammar. To refer to a production defined in the same definition use [ref] | |
| 10 /// with the function reference as the first argument. | |
| 11 /// | |
| 12 /// Consider the following example to parse a list of numbers: | |
| 13 /// | |
| 14 /// class ListGrammarDefinition extends GrammarDefinition { | |
| 15 /// start() => ref(list).end(); | |
| 16 /// list() => ref(element) & char(',') & ref(list) | |
| 17 /// | ref(element); | |
| 18 /// element() => digit().plus().flatten(); | |
| 19 /// } | |
| 20 /// | |
| 21 /// Since this is plain Dart code, common refactorings such as renaming a produc
tion | |
| 22 /// updates all references correctly. Also code navigation and code completion | |
| 23 /// works as expected. | |
| 24 /// | |
| 25 /// To attach custom production actions you might want to further subclass your | |
| 26 /// grammar definition and override overriding the necessary productions defined | |
| 27 /// in the superclass: | |
| 28 /// | |
| 29 /// class ListParserDefinition extends ListGrammarDefinition { | |
| 30 /// element() => super.element().map((value) => int.parse(value)); | |
| 31 /// } | |
| 32 /// | |
| 33 /// Note that productions can be parametrized. Define such productions with posi
tional | |
| 34 /// arguments and reference to multiple instances by passing the arguments to [r
ef]. | |
| 35 /// | |
| 36 /// Consider extending the above grammar with a parametrized token production: | |
| 37 /// | |
| 38 /// class TokenizedListGrammarDefinition extends GrammarDefinition { | |
| 39 /// start() => ref(list).end(); | |
| 40 /// list() => ref(element) & ref(token, char(',')) & ref(list) | |
| 41 /// | ref(element); | |
| 42 /// element() => ref(token, digit().plus()); | |
| 43 /// token(p) => p.token().trim(); | |
| 44 /// } | |
| 45 abstract class GrammarDefinition { | |
| 46 const GrammarDefinition(); | |
| 47 | |
| 48 /// The starting production of this definition. | |
| 49 Parser start(); | |
| 50 | |
| 51 /// Returns a parser reference to a production defined by a [function]. | |
| 52 /// | |
| 53 /// The optional arguments parametrize the called production. | |
| 54 Parser ref(Function function, [arg1, arg2, arg3, arg4, arg5, arg6]) { | |
| 55 var arguments = [arg1, arg2, arg3, arg4, arg5, arg6] | |
| 56 .takeWhile((each) => each != null) | |
| 57 .toList(growable: false); | |
| 58 return new _Reference(function, arguments); | |
| 59 } | |
| 60 | |
| 61 /// Builds a composite parser from this definition. | |
| 62 /// | |
| 63 /// The optional [start] reference specifies a different starting production i
nto | |
| 64 /// the grammar. The optional [arguments] list parametrizes the called product
ion. | |
| 65 Parser build({Function start: null, List arguments: const []}) { | |
| 66 return _resolve( | |
| 67 new _Reference(start != null ? start : this.start, arguments)); | |
| 68 } | |
| 69 | |
| 70 /// Internal helper to resolve a complete parser graph. | |
| 71 Parser _resolve(_Reference reference) { | |
| 72 var mapping = new Map(); | |
| 73 | |
| 74 Parser _dereference(_Reference reference) { | |
| 75 var parser = mapping[reference]; | |
| 76 if (parser == null) { | |
| 77 var references = [reference]; | |
| 78 parser = reference.resolve(); | |
| 79 while (parser is _Reference) { | |
| 80 if (references.contains(parser)) { | |
| 81 throw new StateError('Recursive references detected: $references'); | |
| 82 } | |
| 83 references.add(parser); | |
| 84 parser = parser.resolve(); | |
| 85 } | |
| 86 for (var each in references) { | |
| 87 mapping[each] = parser; | |
| 88 } | |
| 89 } | |
| 90 return parser; | |
| 91 } | |
| 92 | |
| 93 var todo = [_dereference(reference)]; | |
| 94 var seen = new Set.from(todo); | |
| 95 | |
| 96 while (todo.isNotEmpty) { | |
| 97 var parent = todo.removeLast(); | |
| 98 for (var child in parent.children) { | |
| 99 if (child is _Reference) { | |
| 100 var referenced = _dereference(child); | |
| 101 parent.replace(child, referenced); | |
| 102 child = referenced; | |
| 103 } | |
| 104 if (!seen.contains(child)) { | |
| 105 seen.add(child); | |
| 106 todo.add(child); | |
| 107 } | |
| 108 } | |
| 109 } | |
| 110 | |
| 111 return mapping[reference]; | |
| 112 } | |
| 113 } | |
| 114 | |
| 115 /// A helper to build a parser from a {@link GrammarDefinition}. | |
| 116 class GrammarParser extends DelegateParser { | |
| 117 GrammarParser(GrammarDefinition definition) : super(definition.build()); | |
| 118 } | |
| 119 | |
| 120 class _Reference extends Parser { | |
| 121 final Function function; | |
| 122 final List arguments; | |
| 123 | |
| 124 _Reference(this.function, this.arguments); | |
| 125 | |
| 126 Parser resolve() => Function.apply(function, arguments); | |
| 127 | |
| 128 @override | |
| 129 bool operator ==(other) { | |
| 130 if (other is! _Reference || | |
| 131 other.function != function || | |
| 132 other.arguments.length != arguments.length) { | |
| 133 return false; | |
| 134 } | |
| 135 for (var i = 0; i < arguments.length; i++) { | |
| 136 var a = arguments[i], | |
| 137 b = other.arguments[i]; | |
| 138 if (a is Parser && a is! _Reference && b is Parser && b is! _Reference) { | |
| 139 // for parsers do a deep equality check | |
| 140 if (!a.isEqualTo(b)) { | |
| 141 return false; | |
| 142 } | |
| 143 } else { | |
| 144 // for everything else just do standard equality | |
| 145 if (a != b) { | |
| 146 return false; | |
| 147 } | |
| 148 } | |
| 149 } | |
| 150 return true; | |
| 151 } | |
| 152 | |
| 153 @override | |
| 154 int get hashCode => function.hashCode; | |
| 155 | |
| 156 @override | |
| 157 Parser copy() => throw new UnsupportedError('References cannot be copied.'); | |
| 158 | |
| 159 @override | |
| 160 Result parseOn(Context context) => throw new UnsupportedError('References cann
ot be parsed.'); | |
| 161 } | |
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Chromium Code Reviews
Issue 2989763002:
Update charted to 0.4.8 and roll (Closed)
