I haven’t tried this yet, but it looks wicked.  You can write custom error messages to help you debug your programs.

Let’s say during your datastep, you have an If Statement:

 if daysout lt 0 then do;

        error ‘Days checked out less than zero: ‘ itemid=

            checkout= daysout=;

        end;

The SAS Log will look like:

    17     if daysout lt 0 then do;
    18      error ‘Days checked out less than zero: ‘ itemid=
    19         checkout= daysout=;
    20     end;
    21 run;

    Days checked out less than zero: itemid=LIB0397
    checkout=05/14/2001 daysout=-31
    itemid=LIB0397 checkout=05/14/2001 duedate=06/14/2001
    empno=001005 canrenew=Y nrenew=0

    NOTE: There were 446 observations read from the dataset CORPLIB.CIRCUL.
    NOTE: The data set WORK.USAGE has 446 observations and 9 variables.
    NOTE: DATA statement used: real time 0.22 seconds