1 betto_lexical

Lexical text utilities for Dart and Flutter — tokenization, stemming, and stop-word filtering. Part of the Bettongia open-source family.

1.1 Features

• Tokenizers — RegExpTokenizer (pure Dart), IcuTokenizer (UAX #29 via system ICU, superior Unicode/CJK coverage), and BrowserTokenizer (web). createDefaultTokenizer() selects the best tokeniser for the current platform automatically.
• Stemmer — Snowball-based stemmer via Stemmer(locale). Currently supports English (en).
• Stop words — getStopWords(locale) returns the Stopwords set for a locale. Covers 58 languages.

1.2 Platform support

1.3 Installation

dependencies:
  betto_lexical: ^0.1.0-dev.1

1.4 Usage

1.4.1 Tokenization

import 'package:betto_lexical/betto_lexical.dart';

// Platform-aware default (IcuTokenizer on native, BrowserTokenizer on web).
final tokeniser = createDefaultTokenizer();
final tokens = tokeniser.tokenise('The quick brown fox');
// → ['The', 'quick', 'brown', 'fox']

// Pure-Dart alternative — works everywhere, English-oriented.
final regexpTokenizer = RegExpTokenizer();

1.4.2 Stemming

import 'package:betto_lexical/betto_lexical.dart';
import 'package:intl/locale.dart';

final stemmer = Stemmer(Locale.parse('en'));
print(stemmer.stem('running')); // → 'run'
print(stemmer.stem('libraries')); // → 'librari'

1.4.3 Stop words

import 'package:betto_lexical/betto_lexical.dart';
import 'package:intl/locale.dart';

final stopWords = getStopWords(Locale.parse('en'));
final tokens = ['the', 'quick', 'brown', 'fox'];
final filtered = tokens.where((t) => !stopWords.listing.contains(t)).toList();
// → ['quick', 'brown', 'fox']

Stop words are available for: Afrikaans, Arabic, Bulgarian, Bengali, Breton, Catalan, Czech, Danish, German, Greek, English, Esperanto, Spanish, Estonian, Basque, Persian, Finnish, French, Irish, Galician, Gujarati, Hausa, Hebrew, Hindi, Croatian, Hungarian, Armenian, Indonesian, Italian, Japanese, Korean, Kurdish, Latin, Lithuanian, Latvian, Marathi, Malay, Dutch, Norwegian, Polish, Portuguese, Romanian, Russian, Slovak, Slovenian, Somali, Sotho, Swedish, Swahili, Thai, Tagalog, Turkish, Ukrainian, Urdu, Vietnamese, Yoruba, Chinese, and Zulu.

Stop-word data is sourced from stopwords-iso, a community collection of stop-word lists for 50+ languages published under the MIT licence.

1.4.4 Regenerating stop words

The files under lib/src/stopwords/ and lib/src/stopwords.g.dart are generated from the upstream dataset and must not be edited by hand. To update them, run:

make generate_stopwords

This downloads the latest stopwords-iso.json from the stopwords-iso repository, then emits one part of file per language plus a thin main file that declares the Stopwords enum. Re-run whenever the upstream dataset is updated.

1.5 License

Apache 2.0 — see LICENSE.

The snowball_stemmer package is used for stemming and is subject to its own licence.