Add ExactMatcher

lib/src/preset_matchers.dart

@@ -62,3 +62,24 @@ class TelMatcher extends TextMatcher {
         r')(?!\d)',
   ]);
 }
+
+/// A variant of [TextMatcher] for parsing strings that exactly match
+/// any of the strings in the passed list.
+///
+/// {@template textParser.ExactMatcher}
+/// ```dart
+/// TextParser(
+///   matchers: [
+///     ExactMatcher(['e.g.', 'C++']),
+///   ],
+/// )
+/// ```
+/// {@endtemplate}
+class ExactMatcher extends TextMatcher {
+  /// Creates an [ExactMatcher] for parsing strings that exactly match
+  /// any of the strings in the passed list.
+  ///
+  /// {@macro textParser.ExactMatcher}
+  ExactMatcher(Iterable<String> strings)
+      : super(strings.map(RegExp.escape).join('|'));
+}

test/matchers/exact_matcher_test.dart

@@ -0,0 +1,29 @@
+import 'package:test/test.dart';
+
+import 'package:text_parser/text_parser.dart';
+
+extension on ExactMatcher {
+  RegExp toRegExp() {
+    return RegExp(pattern);
+  }
+}
+
+void main() {
+  test('Strings using reserved characters match exactly same strings', () {
+    const input = 'Assembly BASIC C++? Dart (^*^)/';
+    final regExp = ExactMatcher(const ['(^*^)/', 'C++']).toRegExp();
+    final matches = regExp.allMatches(input).toList();
+    expect(matches, hasLength(2));
+    expect(input.substring(matches[0].start, matches[0].end), 'C++?');
+    expect(input.substring(matches[1].start, matches[1].end), '(^*^)/');
+  });
+
+  test('Reserved characters are escaped and used as ordinary characters', () {
+    const input = 'ABCDEF AB.DE+';
+    final regExp = ExactMatcher(const ['B.D', 'E+']).toRegExp();
+    final matches = regExp.allMatches(input).toList();
+    expect(matches, hasLength(2));
+    expect(input.substring(matches[0].start, matches[0].end), 'B.D');
+    expect(input.substring(matches[1].start, matches[1].end), 'E+');
+  });
+}