static void WriteSequencePoint (TextWriter writer, SequencePoint sequence_point)
		{
			writer.Write (".line {0},{1}:{2},{3} '{4}'",
				sequence_point.StartLine,
				sequence_point.EndLine,
				sequence_point.StartColumn,
				sequence_point.EndColumn,
				sequence_point.Document.Url);
		}
		public InstructionSymbol (int offset, SequencePoint sequencePoint)
		{
			this.Offset = offset;
			this.SequencePoint = sequencePoint;
		}
		static void ReadLine (PdbLine line, Document document, InstructionMapper mapper)
		{
			var instruction = mapper ((int) line.offset);
			if (instruction == null)
				return;

			var sequence_point = new SequencePoint (document);
			sequence_point.StartLine = (int) line.lineBegin;
			sequence_point.StartColumn = (int) line.colBegin;
			sequence_point.EndLine = (int) line.lineEnd;
			sequence_point.EndColumn = (int) line.colEnd;

			instruction.SequencePoint = sequence_point;
		}