parseOn method
Parses the given context.
Overridden in concrete subclasses to implement the parser-specific logic.
Takes a parse context and returns the resulting context, which is either
a Success or Failure context.
Implementation
@override
Result<Match> parseOn(Context context) {
final result = pattern.matchAsPrefix(context.buffer, context.position);
if (result == null) return context.failure(message);
return context.success(result, result.end);
}