This package exposes aStringScanner type that makes it easy to parse a stringusing a series ofPatterns. For example:

import 'dart:math' as math;import 'package:string_scanner/string_scanner.dart';num parseNumber(String source) {  // Scan a number ("1", "1.5", "-3").  final scanner = StringScanner(source);  // [Scanner.scan] tries to consume a [Pattern] and returns whether or not it  // succeeded. It will move the scan pointer past the end of the pattern.  final negative = scanner.scan('-');  // [Scanner.expect] consumes a [Pattern] and throws a [FormatError] if it  // fails. Like [Scanner.scan], it will move the scan pointer forward.  scanner.expect(RegExp(r'\d+'));  // [Scanner.lastMatch] holds the [MatchData] for the most recent call to  // [Scanner.scan], [Scanner.expect], or [Scanner.matches].  var number = num.parse(scanner.lastMatch![0]!);  if (scanner.scan('.')) {    scanner.expect(RegExp(r'\d+'));    final decimal = scanner.lastMatch![0]!;    number += int.parse(decimal) / math.pow(10, decimal.length);  }  // [Scanner.expectDone] will throw a [FormatError] if there's any input that  // hasn't yet been consumed.  scanner.expectDone();  return (negative ? -1 : 1) * number;}