parser_builder_lite #

Parser Builder Lite is a lightweight and uncomplicated parser combinator builder (source code generator).

Version: 0.6.5

What is it and what is it for? #

Parser Builder is intended to quickly implement (and test) parsers through source code templates.
The main features and advantage:

• A very simple builder is used to build parsers
• Parsers are generated into source code
• The generated parsers are very fast and efficient
• The SmartChoice parser builder increases the performance of parsing by looking one character ahead.
• The error reporting system is very flexible and informative
• Convenient and easy debugging of the parsing process
• A simple and convenient test generator is included

Parser builder example #

A typical example of a parser builder (with static template).

import '../helper.dart';
import '../parser_builder.dart';

class Many<I, O> extends ParserBuilder<I, List<O>> {
  static const _template = '''
final list = <{{O}}>[];
while (true) {
  final r1 = {{p1}}(state);
  if (r1 == null) {
    break;
  }
  list.add(r1.value);
}
return Result(list);''';

  final ParserBuilder<I, O> p;

  const Many(this.p);

  @override
  String buildBody(BuildContext context) {
    return render(_template, {
      'O': '$O',
      'p1': p.build(context).name,
    });
  }
}

Parser builder usage example #

A typical example of using a parser builder.

const _object = Named(
    '_object',
    Mapped(
      Tuple3(
        _openBrace,
        _keyValues,
        _closeBrace,
      ),
      Expr<Map<String, Object?>>(r'Map.fromEntries({{0}}.$2)'),
    ));

An example of the generated source code.
As you can see, there is not a lot of source code, just as much as is generated from the template.

Result<(String, List<MapEntry<String, Object?>>, String)>? _p$0(
    State<String> state) {
  final pos = state.pos;
  final r1 = _openBrace(state);
  if (r1 != null) {
    final r2 = _keyValues(state);
    if (r2 != null) {
      final r3 = _closeBrace(state);
      if (r3 != null) {
        return Result((r1.value, r2.value, r3.value));
      }
    }
  }
  state.pos = pos;
  return null;
}

Result<Map<String, Object?>>? _object(State<String> state) {
  final r1 = _p$0(state);
  if (r1 != null) {
    final v = Map.fromEntries(r1.value.$2);
    return Result(v);
  }
  return null;
}

Fast build example #

A typical example of a source code builder.

Future<void> main(List<String> args) async {
  await fastBuild(
    context: BuildContext(
      allocator: Allocator('_p'),
      output: StringBuffer(),
    ),
    filename: 'example/json_parser.dart',
    footer: __footer,
    header: __header,
    parsers: [json, _value_],
  );
}

Error reporting #

All errors are generated automatically.
But if you need elegant error messages, then you can use the built-in parsers for this, which generate more informative error messages.
Or you can always write your own parser builder for this purpose.
Moreover, this parser builder will be the same as all the others, no different from any other.

Error handling customization example:

const _hexValueChecked = Named(
    '_hexValueChecked',
    ReplaceErrors(
      _hexValue,
      Expr<Object?>(
          '''ErrorMessage({{1}} - {{0}}, 'Expected 4 digit hexadecimal number')'''),
    ));

Data source (JSON):

"abc\u123  "

Error report:

line 1, column 7: Expected 4 digit hexadecimal number
"abc\u123  "
      ^^^

An example of standard error messages.
Error messages will directly depend on the selected parsing algorithm.

Data source (JSON):

{"rocket": "🚀 flies to the stars}

Error report:

Unhandled exception:
line 1, column 35: Unexpected end of file
{"rocket": "🚀 flies to the stars}
                                  ^

line 1, column 35: Expected '\', '\u', '"'
{"rocket": "🚀 flies to the stars}
                                  ^

Parser test generator #

Example of usage:

import 'package:parser_builder_lite/allocator.dart';
import 'package:parser_builder_lite/fast_build.dart';
import 'package:parser_builder_lite/parser/char.dart';
import 'package:parser_builder_lite/parser/many.dart';
import 'package:parser_builder_lite/parser/preceded.dart';
import 'package:parser_builder_lite/parser_builder.dart';
import 'package:parser_builder_lite/parser_tester.dart';

void main(List<String> args) async {
  await _generate();
}

const _footer = '''
''';

const _header = '''
// ignore_for_file: non_constant_identifier_names
// ignore_for_file: inference_failure_on_collection_literal
// ignore_for_file: unnecessary_cast

import 'package:test/test.dart' hide escape;
''';

const _prefix = '';

Future<void> _generate() async {
  final context = BuildContext(
    allocator: Allocator('_'),
    output: StringBuffer(),
  );
  final tester = ParserTester<String>(
    context: context,
    localOutput: StringBuffer(),
  );
  tester.addTest('Many', const Many(Char(0x31)), (parserName, parser) {
    final buffer = StringBuffer();
    final t1 = ParserTest(
      allocator: Allocator(_prefix),
      context: context,
      output: buffer,
      parser: parser,
      parserName: parserName,
    );
    t1.testSuccess(
      source: '1112',
      result: [0x31, 0x31, 0x31],
      pos: 3,
    );
    t1.testSuccess(
      source: '',
      result: [],
      pos: 0,
    );
    t1.testSuccess(
      source: '2',
      result: [],
      pos: 0,
    );
    return buffer.toString();
  });

  tester.addTest('Preceded', const Preceded(Char(0x31), Char(0x32)),
      (parserName, parser) {
    final buffer = StringBuffer();
    final t1 = ParserTest(
      allocator: Allocator(_prefix),
      context: context,
      output: buffer,
      parser: parser,
      parserName: parserName,
    );
    t1.testSuccess(
      source: '123',
      result: 0x32,
      pos: 2,
    );
    t1.testFailure(
      source: '',
      failPos: 0,
      pos: 0,
      errors: [errorUnexpectedEof],
    );
    t1.testFailure(
      source: '1',
      failPos: 1,
      pos: 0,
      errors: [errorUnexpectedEof],
    );
    t1.testFailure(
      source: '2',
      failPos: 0,
      pos: 0,
      errors: [errorExpectedChar],
    );
    return buffer.toString();
  });

  await fastBuild(
    context: context,
    parsers: [...tester.parsers],
    filename: 'example/simple_test.dart',
    addErrorMessageCode: false,
    footer: _footer,
    header: _header + tester.generate(),
  );
}

Generated tests (part of this file):

// ignore_for_file: non_constant_identifier_names
// ignore_for_file: inference_failure_on_collection_literal
// ignore_for_file: unnecessary_cast

import 'package:test/test.dart' hide escape;

void main() {
  _test();
}

void _test() {
  // Many
  _test_Many$0();
  // Preceded
  _test_Preceded$0();
}

void _test_Many$0() {
  // Many
  test('Many', () {
    final state$0 = State('1112');
    final result$0 = _Many$0(state$0);
    expect(result$0 != null, true,
        reason: 'Testing \'result != null\' failed, source: \'1112\'');
    final value$0 = result$0!.value;
    expect(value$0, [49, 49, 49],
        reason: 'Testing \'result.value\' failed, source: \'1112\'');
    expect(state$0.pos, 3,
        reason: 'Testing \'state.pos\' failed, source: \'1112\'');
    final state$1 = State('');
    final result$1 = _Many$0(state$1);
    expect(result$1 != null, true,
        reason: 'Testing \'result != null\' failed, source: \'\'');
    final value$1 = result$1!.value;
    expect(value$1, [],
        reason: 'Testing \'result.value\' failed, source: \'\'');
    expect(state$1.pos, 0,
        reason: 'Testing \'state.pos\' failed, source: \'\'');
    final state$2 = State('2');
    final result$2 = _Many$0(state$2);
    expect(result$2 != null, true,
        reason: 'Testing \'result != null\' failed, source: \'2\'');
    final value$2 = result$2!.value;
    expect(value$2, [],
        reason: 'Testing \'result.value\' failed, source: \'2\'');
    expect(state$2.pos, 0,
        reason: 'Testing \'state.pos\' failed, source: \'2\'');
  });
}

void _test_Preceded$0() {
  // Preceded
  test('Preceded', () {
    final state$0 = State('123');
    final result$0 = _Preceded$0(state$0);
    expect(result$0 != null, true,
        reason: 'Testing \'result != null\' failed, source: \'123\'');
    final value$0 = result$0!.value;
    expect(value$0, 50,
        reason: 'Testing \'result.value\' failed, source: \'123\'');
    expect(state$0.pos, 2,
        reason: 'Testing \'state.pos\' failed, source: \'123\'');
    final state$1 = State('');
    final result$1 = _Preceded$0(state$1);
    expect(result$1 == null, true,
        reason: 'Testing \'result == null\' failed, source: \'\'');
    expect(state$1.pos, 0,
        reason: 'Testing \'state.pos\' failed, source: \'\'');
    expect(state$1.failPos, 0,
        reason: 'Testing \'state.failPos\' failed, source: \'\'');
    expect(state$1.errors.length, 1,
        reason: 'Testing \'state.errors.length\' failed, source: \'\'');
    expect(state$1.errors[0], isA<ErrorUnexpectedEof>(),
        reason: 'Testing \'state.error\' failed, source: \'\'');
    final state$2 = State('1');
    final result$2 = _Preceded$0(state$2);
    expect(result$2 == null, true,
        reason: 'Testing \'result == null\' failed, source: \'1\'');
    expect(state$2.pos, 0,
        reason: 'Testing \'state.pos\' failed, source: \'1\'');
    expect(state$2.failPos, 1,
        reason: 'Testing \'state.failPos\' failed, source: \'1\'');
    expect(state$2.errors.length, 1,
        reason: 'Testing \'state.errors.length\' failed, source: \'1\'');
    expect(state$2.errors[0], isA<ErrorUnexpectedEof>(),
        reason: 'Testing \'state.error\' failed, source: \'1\'');
    final state$3 = State('2');
    final result$3 = _Preceded$0(state$3);
    expect(result$3 == null, true,
        reason: 'Testing \'result == null\' failed, source: \'2\'');
    expect(state$3.pos, 0,
        reason: 'Testing \'state.pos\' failed, source: \'2\'');
    expect(state$3.failPos, 0,
        reason: 'Testing \'state.failPos\' failed, source: \'2\'');
    expect(state$3.errors.length, 1,
        reason: 'Testing \'state.errors.length\' failed, source: \'2\'');
    expect(state$3.errors[0], isA<ErrorExpectedChar>(),
        reason: 'Testing \'state.error\' failed, source: \'2\'');
  });
}

Performance #

Test failures

Parse 20 times: E:\prj\test_json\bin\data\canada.json (2251.05 Kb)
Dart SDK JSON : k: 2.26, 53.87 MB/s, 797.0740 ms (42.15%),
JSON Parser: k: 1.00, 121.52 MB/s, 353.3200 ms (18.69%),

Parse 20 times: E:\prj\test_json\bin\data\citm_catalog.json (1727.03 Kb)
Dart SDK JSON : k: 1.00, 109.12 MB/s, 301.8860 ms (38.28%),
JSON Parser: k: 1.44, 75.82 MB/s, 434.4810 ms (55.09%),

Parse 20 times: E:\prj\test_json\bin\data\twitter.json (567.93 Kb)
Dart SDK JSON : k: 1.00, 68.22 MB/s, 158.7850 ms (57.10%),
JSON Parser: k: 1.22, 55.85 MB/s, 193.9450 ms (69.75%),

OS: Њ ©Єа®б®дв Windows 10 Pro 10.0.19045
Kernel: Windows_NT 10.0.19045
Processor (4 core) Intel(R) Core(TM) i5-3450 CPU @ 3.10GHz