70 lines
1.7 KiB
Dart
70 lines
1.7 KiB
Dart
import 'dart:io';
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import 'package:combinator/combinator.dart';
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import 'package:string_scanner/string_scanner.dart';
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Parser jsonGrammar() {
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var expr = reference();
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// Parse a number
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var number = match<num>(new RegExp(r'-?[0-9]+(\.[0-9]+)?'),
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errorMessage: 'Expected a number.')
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.value(
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(r) => num.parse(r.span.text),
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);
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// Parse a string (no escapes supported, because lazy).
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var string =
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match(new RegExp(r'"[^"]*"'), errorMessage: 'Expected a string.').value(
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(r) => r.span.text.substring(1, r.span.text.length - 1),
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);
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// Parse an array
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var array = expr
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.space()
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.separatedByComma()
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.surroundedBySquareBrackets(defaultValue: []);
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// KV pair
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var keyValuePair = chain([
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string.space(),
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match(':').space(),
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expr.error(errorMessage: 'Missing expression.'),
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]).castDynamic().cast<Map>().value((r) => {r.value[0]: r.value[2]});
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// Parse an object.
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var object = keyValuePair
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.separatedByComma()
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.castDynamic()
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.surroundedByCurlyBraces(defaultValue: {});
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expr.parser = longest(
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[
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array,
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number,
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string,
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object.error(),
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],
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errorMessage: 'Expected an expression.',
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).space();
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return expr.foldErrors();
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}
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main() {
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var JSON = jsonGrammar();
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while (true) {
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stdout.write('Enter some JSON: ');
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var line = stdin.readLineSync();
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var scanner = new SpanScanner(line, sourceUrl: 'stdin');
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var result = JSON.parse(scanner);
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if (!result.successful) {
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for (var error in result.errors) {
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print(error.toolString);
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print(error.span.highlight(color: true));
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}
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} else
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print(result.value);
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}
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}
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