Update charted to 0.4.8 and roll

packages/petitparser/lib/src/petitparser/context.dart

-part of petitparser;
-
-/// An immutable parse context.
-class Context {
-  const Context(this.buffer, this.position);
-
-  /// The buffer we are working on.
-  final buffer;
-
-  /// The current position in the buffer.
-  final int position;
-
-  /// Returns a result indicating a parse success.
-  Result success(result, [int position]) {
-    return new Success(buffer, position == null ? this.position : position, result);
-  }
-
-  /// Returns a result indicating a parse failure.
-  Result failure(String message, [int position]) {
-    return new Failure(buffer, position == null ? this.position : position, message);
-  }
-
-  /// Returns a human readable string of the current context.
-  String toString() => 'Context[${toPositionString()}]';
-
-  /// Returns the line:column if the input is a string, otherwise the position.
-  String toPositionString() => Token.positionString(buffer, position);
-}
-
-/// An immutable parse result.
-abstract class Result extends Context {
-  const Result(buffer, position) : super(buffer, position);
-
-  /// Returns [true] if this result indicates a parse success.
-  bool get isSuccess => false;
-
-  /// Returns [true] if this result indicates a parse failure.
-  bool get isFailure => false;
-
-  /// Returns the parse result of the current context.
-  get value;
-
-  /// Returns the parse message of the current context.
-  String get message;
-}
-
-/// An immutable parse result in case of a successful parse.
-class Success extends Result {
-  const Success(buffer, position, this.value) : super(buffer, position);
-
-  @override
-  bool get isSuccess => true;
-
-  @override
-  final value;
-
-  @override
-  String get message => null;
-
-  @override
-  String toString() => 'Success[${toPositionString()}]: $value';
-}
-
-/// An immutable parse result in case of a failed parse.
-class Failure extends Result {
-  const Failure(buffer, position, this.message) : super(buffer, position);
-
-  @override
-  bool get isFailure => true;
-
-  @override
-  get value => throw new ParserError(this);
-
-  @override
-  final String message;
-
-  @override
-  String toString() => 'Failure[${toPositionString()}]: $message';
-}
-
-/// An exception raised in case of a parse error.
-class ParserError extends Error {
-  final Failure failure;
-
-  ParserError(this.failure);
-
-  @override
-  String toString() => '${failure.message} at ${failure.toPositionString()}';
-}