ICL Exceptions

Error conditions and other unexpected events are referred to as Exceptions in ICL. When such a condition is detected in direct mode a message is output. For example, if we enter a statement which results in an error

    ICL> =SQRT(-1)
    SQUROONEG   Square Root of Negative Number
    ICL>

We get a message consisting of the name of the exception (SQUROONEG) and a description of the nature of the exception. A full list of ICL exceptions is given in appendix C.

If the error occurs within a procedure the message contains a little more information. As an example, if we use our square root procedure of chapter 3 with an invalid value we get the following messages:

    ICL> SQUARE_ROOT (-1)
    SQUROONEG   Square Root of Negative Number
    In Procedure: SQUARE_ROOT
    At Statement: PRINT  The Square Root of (X) is (SQRT(X))
    ICL>

If one procedure is called by another, the second procedure will also be listed in the error message. If we run the following procedure

    PROC TABLE
    {  Print a table of Square roots from 5 down to -5  }
       LOOP FOR I = 5 TO -5 STEP -1
         SQUARE_ROOT (I)
       END LOOP
    END PROC

we get

    ICL> TABLE
    The Square Root of 5 is 2.236068
    The Square Root of 4 is 2
    The Square Root of 3 is 1.732051
    The Square Root of 2 is 1.414214
    The Square Root of 1 is 1
    The Square Root of 0 is 0
    SQUROONEG   Square Root of Negative Number
    In Procedure: SQUARE_ROOT
    At Statement: PRINT  The Square Root of (X) is (SQRT(X))
    Called by: TABLE
    ICL>