Add a string_scanner package.

This code has been pulled out of the Shelf package.

R=kevmoo@google.com

Review URL: https://codereview.chromium.org//213833013

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/string_scanner@34665 260f80e4-7a28-3924-810f-c04153c831b5
6 files changed
tree: 1526368e7a7ed6fa4bffb8f128288ead4d859c1a
  1. lib/
  2. test/
  3. LICENSE
  4. pubspec.yaml
  5. README.md
README.md

This package exposes a StringScanner type that makes it easy to parse a string using a series of Patterns. For example:

import 'dart:math';

import 'package:string_scanner/string_scanner.dart';

num parseNumber(String source) {
  // Scan a number ("1", "1.5", "-3").
  var scanner = new 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.
  var 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(new RegExp(r"\d+"));

  // [Scanner.lastMatch] holds the [MatchData] for the most recent call to
  // [Scanner.scan], [Scanner.expect], or [Scanner.matches].
  var number = int.parse(scanner.lastMatch[0]);

  if (scanner.scan(".")) {
    scanner.expect(new RegExp(r"\d+"));
    var 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;
}