I think there is an error
public virtual void Interpret(GCodeFile file, InterpretArgs args)
{
IEnumerable<GCodeLine> lines_enum =
(args.HasTypeFilter) ? file.AllLines() : file.AllLinesOfType(args.eTypeFilter);
Should be
(args.HasTypeFilter) ? file.AllLinesOfType(args.eTypeFilter) : file.AllLines() :;