Calling functions from XSLTs

Hi All,

 Is there any way of calling self defined functions from within an XSLT
code? AFAIK one can invoke 3 libraries through .NET (using scripts) -
System, System.XML and MSCoreLib. I would like to access my own
functions and datastructres from within the scripts in XSLTs. Is there
any way to do that?

Thanks
amit