How to check for and trap a CAS error in a program?

[BruceH]

Thanks Tim.

Actually it is the part() function that I want to trap and it can return a string legitimately.

After reading Parisse's suggestion, it occurred to me that rather than try and trap the error from part() in my main code, I could just use a separate #cas...#end bracketed function which calls part() with 1, 2, 3, .. etc until it fails and then return the max value to use as the loop upper bound in my main code with no worries about errors.