Writing a function that can take a financial time series or a vector

I am new to Matlab, and I trying to write a function that can accept either a financial time series or a vector. Something like:

   function y = mydiff(x)
      if istimeseries(x)
         vec = fts2mat(x.CLOSE);
      else
         vec = x;
      end

      y = diff(vec);
   end

I'm at a loss, however, on what to put in place of the istimeseries test. Is this possible?

Thanks in advance for the help.

Answer 1

[Rick Rosson]

   if isa(x,'timeseries')
       ...
   else
       ...
   end

[Doug]

That worked like a charm. For the record, the class for a financial time series appears to be 'fints' and not 'timeseries' as I had assumed.