Custom Function

In release 9.2 you can write your own custom functions.
Here's a sample how.

/*
   Custom Function (vanaf SAS 9.2)
*/ 

proc fcmp outlib=sasuser.funcs.trial;
  function std (intervention_day, event_day);
    if event_date < intervention_day then
   return(event_date - intervention_date);
 else
   return (event_date - intervention_date + 1);
  endsub;
run;

options cmplib = sasuser.funcs.trial;

data _null_;
  start = '15Feb2006'd;
  today = '27Mar2006'd;

  sd = std(start, today);

  put sd=;
run;